Duplicates and missing photos when exporting | Lightroom CC version 6.4

[Bailey30795610bxiq]

Please help!

I have seen other posts (several years old) about a similar issue and have spent hours working with IT chat, with no luck.  

When exporting photos from Lightroom CC (not classic) to my external harddrive, I am getting duplicates of some photos and other photos are skipped. For example, when exporting photos 1-10, I have 6 copies of photo 1 and no copies of photos 7-10.
Some background:

• All photos are originally imported as RAWs to lightroom, edited with a preset and tweaking.
• All photos are then edited in Photoshop and saved back into Lightroom, creating a stacked photo (automatically) in Lightroom. 
• I have the most up-to-date versions of Lightroom, Photoshop, and Windows 11. 
• I have uninstalled and reinstalled both programs, restarted my computer, and reset my wifi. No luck on any accounts. 

I have been editing photos the same way for the past two years without issue. I just exported a 600+ album last week with no issues. This issue seemed to come out of nowwhere. I've also have stumped the Adobe support team, as the best advice I've received so far is to manually unstack all 700+ photos in this wedding album and download each final photo version individually... Which I don't have time to do for all wedding albums I am editing. 

Thanks so much, 
B.

[Rikk Flohr: Photography]

Greetings, and apologies for the delay.

If you increase the size of your Cache in Prefs>Local Storage, does the issue improve?