Bug with sync and notes
Long story short, my Vivaldi started to freeze immediately after launch and using up all free memory, after some time I think I found the cause.
Looks like sync duplicates notes that have no title, because two of them I had, were duplicated like 200 000 times and sync file was almost 1GB in size.
I deleted sync folder and Vivaldi launched fine.
For now in sync settings I wanted to delete server data but there has to be a lot of crap there because it's deleting it for like three hours now. Can you delete it manually or something?
Bug reported as VB-35453 [Sync] "Notes with empty title are duplicated"