I worked on my laptop in the afternoon and created some new entries into my Zotero account. The computer was on the internet all the time and had plenty of time to synchronize. Then I went to my desktop and expected the new entries to appear there quite soon but even about an hour later, the entries made in the laptop are still not in the PC. Laptop says: Syncing files in my library, 2 remaining. Desktop says Syncing files in my library, 29 remaining. I even have the suspicion that some work done on another desktop has not been synchronized in time.

How can I be sure that all new entries have been entered in the database?
Is there a limit to the number of entries per account?
Is there any problem that 2 windows machines with the same Zotero account active are online at the same time?