Significant System & Mouse lag after high sierra install

Do you have any peripherals attached to your Mac? In that case, remove everything and try with a new start.

If the issue is still there, try to reboot in safe mode Use safe mode to isolate issues with your Mac - Apple Support and see the behaviour. In case still issue, then reset the NVRAM how described in this article: How to reset NVRAM on your Mac - Apple Support and if still there, well give a try with this tool: https://etrecheck.com/ and post here the result.

Similar issue here with a 2017 iMac. Did you find a way to keep you monitor connected? Our computer is a presentation computer that NEEDS to be connected to 2 monitors. I get mouse lag/freezing in 2 separate scenarios:

1. The set up that worked before updating to High Sierra was 2 USB-C to HDMI adapters feeding 2 external monitors. 1 is a TV the other is HDMI to a DVI adapter connecting to a switcher. Disconnecting the HDMI to DVI connection removes the mouse lag
2. I was able to get a lag free system after update by bypassing the switcher and running HDMI straight to a projector BUT the lag reappears if the projector and/or TV are OFF.

Thanks,

It can be that something is going wrong with the update and resetting the SMC and/or the NVRAM usually helps, so if resetting the parameters and the plugin the devices solve the problem is fine. If not, just contact the support: Official Apple Support

The answer from getangar, below, has instructions for resetting the NVRAM and that fixed my problem with a sticky mouse pointer.

My system is a Mac Mini with 16 Gigs memory running High Sierra, the Apple wireless keyboard and mouse.

Agree. It now takes several attempts (clicking and waiving the mouse around) to log on. There are numerous problems like this (iPhoto crashing out during editing being one) with the High Sierra upgrade - I wish I'd not bothered with it. Apple don't like to admit there is anything wrong. I hope these issues will be fixed in the near future.

Feel a little silly that I had forgotten the arrow keys. Thanks.

Oops, had to wait to post this since an Apple alert informed me my post limit was reached and that I needed to wait a bit before it will add my response.

Really? I get emails from Apple notifying me about replies and encouraging a response. The original post generated quite a number of replies, yet apparently Apple isn't so keen on my sitting down when I have time and responding to all that took the time to add to the discussion. Boo, hiss.

Perhaps they will be fixed; it's likely. I want to know why Apple updates have become quite unreliable. When Jobs was around this did not happen, and, if it did, some folks were out looking for new employers. Hope, I assert, is a cousin of something highly addictive, perhaps on a level like nicotine, for example.

Thanks for your help - as suggested I tried using the keyboard to wake up the screen and it is a little quicker than the mouse, although still not back to how it was before the High Sierra upgrade. My main issue though is that Apple are one of the largest and richest companies in the world and should be putting more resources into checking these upgrades more thoroughly before they are released to the public. It's shoddy and unprofessional to expect their customers to find workarounds for them. Anyway thanks again :-)

UPDATE:

Apple Support did some troubleshooting with me and ended up concluding that High Sierra was having some compatibility problems with 3rd party video adapters. I had 2 USB-C to HDMI adapters from Anker. Apple sent me one of their adapters but before I received it the problem went away with the last High Sierra update.

I am adding this post/reply to note that, while the issue cleared up for me temporarily by resetting NVRAM, it returned with a vengence. I'm running High Sierra on my Mac Mini, Late 2012 (maybe that's the issue-older Apple whatevers get left in the dust) and decided to ask how to roll back the update. If I followed the procedure described, I'd have to set aside two or three days to get through it and set up all my apps. Until Apple fixes this issue, I've moved work I'm doing for client to a Linux box. Really prefer my Mac Mini, yet I've got work to do and deadlines to meet. As a one man shop, I cannot spend hours tinkering for solutions.

I do recommend you reset NVRAM as well as PRAM and see if this fixes the problem for you. Perhaps, if you've a newer Mac Mini, iMac or any flavor MacBook this will be the fix. Or, perhaps the newer models are not having this issue.

Maybe Solved...

Am running Private Internet Access (PIA) VPN and it began to act up this morning. Also noticed that when using Enpass, my password manager, I'd have to click several times inside that app before the mouse was recognized.

I uninstalled PIA then uninstalled Enpass. Shutdown the Mac Mini and after a minute or so, restarted it. Following a successful startup, I reinstalled Enpass and set up using iCloud backup data. Decided not to reinstall PIA at this time.

Bottom line: Mouse is no longer sticky or slow. Essentially it's back to normal. Think it might be a good idea to look at third party apps as being the root cause of some of this mouse stickiness. Hope this helps.

UPDATE:

The mouse lag issue has now completely disappeared. I changed nothing, so I'm at a loss to explain this. However, in it's place ( and this is probably a complete coincidence) the over-running fan issue has reappeared, but worse than before as it now does this every 10-20 seconds 24/7. Also had a massive problem with Time Machine backup - took over 5 hours when it normally takes 20 minutes. There is also another problem of random opening of Apps on startup. Will nee to start new threads for these 😢

Also concerned about the new security update - will this cause even more instability in the system 😕

About your complaints:

- good that the mouse issue disappeared, it may have to do with the macOS updates.

- the fans is not uncommon, they react much faster in HSierra. Should not be doing that but it is not uncommon. It is one software that starts checking (I do not know which one, but it happens often when Google updater is on your system, or when you have a software that continuously checks for some changes....)

- TM backup takes much more time after upgrade to HighSierra: almost everything has changed, comes back to normal after one week (at least in my case).

- Random opening of apps at startup: yes, check that in the apps settings and in the User&Groups->LoginItems: most of the settings are changed after the macOs upgrade to HSierra.

- The new security update: necessary for the newly discovered CPU vulnerability (Meltdown and Spectre). This update has to "dig deep": it slows down the computer maybe 1-2%, the update itself takes much longer than "normal", but it is necessary !

Thanks for your quick and comprehensive reply - it's much appreciated.

- Having investigated the fan problem again, some people advised cleaning the fan ventilation slots with a soft brush and and this has actually cured my problem for now. Low tech, but effective!

- I'm about to do another TM back up and hopefully this will be quicker. I suspect that the reason for the slow backup may be my several thousand photos reorganising from iPhoto.

- I had already checked app settings and had nothing in the list. I suspect it is more related to the way I close an app down. If I use a right click and quit rather than the X I've round it seems to avoid the problem.

- I'll get the new update after I've backed up 😁