Updated to 10.13.5, lost Bluetooth

I'm also getting this issue although for me it started with my Apple Bluetooth mouse dropping out which i thought was hardware issue at first and like you performed the reset at boot and profile deletion but it would keep coming back. But now after latest update all Bluetooth devices get dropped when i connect either my iPhone 8 or Ipad Pro and Bluetooth locks up and wont shut down so have to then perform a reboot to get devices back and now have to keep a wired mouse attached for rebooting once Keyboard and mouse disappear. I have reported this as a bug but it now seems it is more widespread and going back to earlier in the year the Mac never had this problem, so this issue has come about during the patching from march.

well if a firmware update was applied then this can affect the bios and so cause issues in that it might not be possible to roll back to earlier as i remember years ago when everyone was having problems with the CD drive stop working in MacBook Pro after an update with myself included had to get new cd drives fitted as the firmware was corrupted on CD drive and no way to then roll back.

Last time i had bluetooth issue was Wednesday when I turned on my Nektar P6 midi controller/Keyboard (USB) and instead of it just connecting like usual I had the spinning colour wheel for a minute and when Midi keyboard finally connected both keyboard and mouse dropped out although this time it notified them dropping out onscreen and was able to stop start bluetooth and fingers crossed it's not actually done it again for the past few days.

Ok Bluetooth just failed again, I found an article on how to reset Bluetooth from the hidden debug menu (shift+Option then select bluetooth) afterwards turned on Audio interface (Presonus Studio 192, USB3) as this caused Bluetooth to crash late Saturday evening (yesterday) and all good followed by turning on my Midi Keyboard still good, so then attached my iPhone 8 and it connected still had bluetooth but noticed iPhone was not backing itself up so launched the menu within iTunes and performed manual Sync and as soon as that started Bluetooth devices disconnected and bluetooth was showing as unavailable. Had to reboot to get everything back.

I hope Apple developers work out what this issue is as my iMac is latest 2017 model and not even a year old but does still have hardware support so I might speak to them and let take a look and in that case i would delete my data for them to access it and if going to do that might just do a rebuild myself and see if issue goes away and if not then let them take it.

Article for Bluetooth Debug: http://osxdaily.com/2015/12/15/reset-bluetooth-hardware-module-mac-osx/

I have also now got my iMac booked in tomorrow for repair as i still have 4 months hardware support, yesterday i rebuilt my iMac and problem still exists although today while i was in Chat with support, we were trying different things to see if it fixed issue and he mentioned about noise causing problems for the BT module. I removed a thunderbolt to USB 3 adaptor i had plugged in as they can cause noise but problem still occurred after it was removed.

the issue for me is also kinda random when it will do it but always seems to be when a USB device is plugged in like iPhone/iPad or turned on.

I'll wait to see what the hardware engineers say tomorrow and if they do replace anything will update here.

My iMac is now fixed and working, many thanks to Stormfront(authorised Apple repairer) as my iMac repair only took 4 days turnaround. It also turned out it was the BT/Wireless module that had become faulty and was replaced under warranty.

Okay, I backed up to TM, connected my wireless keyboard into the iMac through a lightning cable as insurance, and carried out the 10.13.5 software update.

It all updated trouble-free this time. Yowsah.

https://support.apple.com/en-us/HT201295