Sync stuck after old machine died

[N D H]

Lightroom Classic 11.1.

My old machine died, and nothing new has synced since.

I've rebuilt the sync data twice; nothing.

I've looked for the errors in catalog on web, mobile, and LRC, and removed all errors, nothing.

I've found 7 pics "pending" against the machine that died, and I've removed them from all three directions, but still they show as "pending" forever.

Interestingly, new photos, flags, or develop settings pushed from the mobile or web site show up on the LRC master catalog.  But no new photographs, flags, develop settings, etc. have appeared in the mobile catalog since Dec 8 when the old machine died.

I've wasted dozens of hours fiddling with this.

I have ~300k photos in my master library in LRC, of which 170k are synced. 

I'm loath to "delete all synced data", because I know it will take about 4 months to resync everything!

Helpful ideas welcome!

[Rikk Flohr: Photography]

"I've found 7 pics "pending" against the machine that died, and I've removed them from all three directions, but still they show as "pending" forever."

Did you also remove them from the Deleted Items at https://lightroom.adobe.com ? That should clear those orphaned images from the sync queue.