Lightroom Classic not syncing with Lightroom out of the blue

[DUDA BREDA]

Dear users, I use the Lightroom Classic o my Imac macOS Big Sur and since one month ago, LC stopped syncin my new Collections on Lightroom. I tried everything users have repported here, including clicking on Sync Preferences, pushing the button OPTION on Sync Activity and clicling on GENERATE DIAGNOSTIC REPORT and REBUILD SYNC DATA. Btw, these two options could never get completed, it was runninr for over 12 hours nad I gave up. All my files are on my external hard drive, fyi.

Can anyone please help me? 

Thank you

[cmgap]

Please provide more details. How much storage do you have in your plan? Do you need to add more?