I made note of a server I was trying to join with the following error message (same as OP): Could not join server ⚽
Server was not full.
Before trying standard troubleshooting (rebooting, etc.), I closed Origin (right click taskbar icon, Exit) and reopened.
Saw there was an update (new Version 9.3.2.2730 - 237075 - E2-S2-A2-L2), installed and relaunched. Opened in browser (chrome) and tested the same server I was unable to join with success.
I wouldve replied sooner, but I was following last step on my original reply.
Sorry if this did not fix your problem.