LR Classic 7.5 Sync error "bad argument #1 to '?' (number expected, got nil)

Same issue here with MacOS 10.13.6 and LR 7,5

The most problems occur with Pictures from external Drive / NAS. Where are you're Pictures stored?

Add another sync issue for me. The 7.4 downgrade worked. A five minute fix.

+1 for me... same problems with syncing... same great results after installing Classic 7.4.  I wish I had found this thread a lot sooner... I've been having trouble for weeks!  What's interesting is I recently got a new computer- I was running LR Classic 7.5 on my old system without any issues, but when I started using the new comp was when I started having all the sync issues.  That lead me down a path of thinking it was something up on my end, not something up with LR, and damn it if I haven't been near-suicidal feeling hopeless and stranded with no way to get a whole bunch of edits done in LR CC (mobile) to sync to my computer so I could export them and deliver to my clients.

So much time lost... such a simple fix!  The first post here was Aug 26; This issue has been ongoing almost a month now.  Hopefully Adobe is about done patching it and will release their update soon... but I'm a bit concerned they might not be aware of it???  I hadn't seen this thread and started my own help thread... and got the usual 'rebuild sync data' suggestion.  Seems like the 7.5 sync issue should be a known thing by now, and I wish I got the suggestion to install 7.4!
Lightroom CC edits not syncing to Classic

Anyway - thanks to everyone here for sharing their issue, and that 7.4 resolved it!  Finally I can sleep... !

Agreed! Best workaround was install version 7.4.

Previous uninstall is not needed since it will be automatically overwritten by the older version.
Quite easy by the CC App:

Yeah great advise guys.

I have been screaming at Lightroom 7.5 for over 30 hours as it simply doesn't sync any changes. I have just spent 10 mins in the Creative Cloud app (previous versions) and rolled back to 7.4 and everything is syncing up lovely!

Avoid 7.5!

Yes, so this continues.... and I've posted this elsewhere on this community under various different topics at different times.

I included a big list of things I've tried... which I'll happily share if it works for you.... but ultimately, this appears to be waiting for a fix on the Adobe side of the fence.

I actually don't mind in essense if the sync fails.... but, when it does, it would be good to know what to fix and where in order to get it going again. Right now..... it's in the ether.

I'll join them, too. The same problem. Furthermore, new images from Lightroom CC taken with the app will not be transferred to Classic.

Same issue in here (Lightroom Classic 7.5)... really annoying

Same problem here, stuck on 'Syncing ** photos' (The number varies after fix attempts, it's currently 33). I've tried all the suggested fixes that I've been able to find but still same problem. In Preferences>Lightroom Sync I have a list of files in the 'Sync Activity' field, all in blue. They have various references, some say 'bad argument..' some have a reference to lightroom.adobe.com/libraries. If you right click on any of these listings there are two options; 'Show Errors' and 'Remove from All Synced Photographs' Clicking on either of these two options  doesn't seem to do anything either. Tried Alt-clicking rebuild sync data multiple times, this doesn't clear the list for me..

Fix soon please Adobe

I have the same problem. All sync stops