Hard drive showing incorrect used space

Yes, you will, yes it fluctuates, yes and no, snapshots uses what it needs, I have 44MBs in iTunes and it shows 7, yes you can stop it and delete them, but I don't recommend it, you need to use the terminal app, you can type in: tmutil listlocalsnapshots / just to look ... I only keep 40 GBs or less on my BOOT DRIVE ... Do you have everything turned on in iCloud >system preferences? Also do you have OPTIMIZED STORAGE turned on in ABOUT THIS MAC> MANAGE>RECOMMENDATIONS? You do this by going into iTunes>preferences and selecting ADVANCED tab ( make sure your logged in ) then check second tab down OPTIMIZE STORAGE. My photos app show 199MBs in the finder but only 154MBs under about this Mac> Manage storage. No two ways about it, its confusing due to the caching, snapshots and iCloud. Also, do you have auto backup turned on in Time Machine? You may try unchecking it and leave it off for a day, then turn it back on .. Last time I ran disk utility, I counted and watched it go through 20 snapshots, the space is there. If you Get info on your boot, what does that read? The OS eats up 10-14 GBS, My apps use 23GBs and user folder is 6.4GBs - about 41-42 GBs .. so minus that from 250GB SSD, its 208GBs with 5GBs in purgeable memory. My BOOT drive fluctuates between 203-205GBs, it actually adds up.

One last item, I totally forgot, my TM backup froze and quit at some point last month, then I started having some issues, wondering if you may have had that problem or the TM disk ejected unexpectedly. Anyway here is a good link on the thread I read, it explains whats going on and why with other good links for info. It also has the terminal command to ZAP the backups ( again, I don't recommend it ) I also included a screen capture while I was inside Time Machine. You can see it makes files called Macintosh HD@snapshots.localXXXXX. I right clicked at the top of the finder window to get the drop down menu to expose the hidden path, again this is just. FYI and its what I ran into. Says I have 68 GB when I only had 45 GBs and there were 6 of them, when it hit 78GBs, I finally just did a clean install from a bootable thumb drive I made of High Sierra, in the end that was the FIX and system works fine other than it still has glitches and bugs.

https://discussions.apple.com/thread/8090544

High Sierra time machine takes local snapshot backups regardless of whether you have a backup device plugged in or not. The snapshots will go away. I know it’s confusing to get 3 different results on how much disk space you have but this is part of the new APFS system. I had 1Gb cached yesterday and am back to 5.3GB today.

I don't either, but it looks like your having the same issue I had a few weeks back, some of my files were FETCHING where there should have been a user name in permissions. Boot in safe mode ( hold shift while rebooting ) then zapping the PRAM did some magic, but yes those look like snapshots. THIS IS BIG and 99% sure it'll help, I erased my time machine and started fresh, also, kept it from auto backup from the beginning ... that seemed to work. Sorry, so many glitches and bugs, I can't keep up with how I fix them all. Good luck .. I feel your pain my friend, I really do.

Open Terminal, paste the following command, and type your password at the prompt:

sudo mdutil -E /

This will trash the existing Spotlight index and re-index your drive (your Mac sees the current free space based on this calculation). After entering it, restart your Mac, and it should be fine (at least it worked for me).

I have submitted feedback to Apple so hopefully it gets on their radar

Well thats all partially good news, I'm glad you made headway. Mac OS has gotten a bit out of hand. It's har keeping up with it. Actually my Mail at one point was stuck in the manage storage window, at 180MBs and I NEVER keep more Than 10-20Mbs in there. I think I had to log out of my account and back in while standing on one leg. Wonky is a good way to describe it, I have used Mac OS since SYSTEM 7.5 (1994-5) and the last 4-5 years have been rough. Things don't refresh and update quickly as they should, files and folders just act weird, settings don't stick, wi-fi issues, software bugs, iCloud etc. UGH... I am using a Mac Pro with 64GB of memory and dual D500s, with all SSD internal and RAID-0 external and things still bog down .. sorry I couldn't be more help, keep me posted, I would like to know how it turns out, hands on, I could do more, bit not over the net. I will keep looking .. Peace

https://discussions.apple.com/thread/7919226

Look at the 2nd or 3rd down and try that link as well .. Sihancox