There must be other factors involved. I've never seen this happen, with over 30 aircraft in the list.
To me it sounds as if Radarbox is geting tied-up in a loop somewhere, so that timeouts don't occur. I just wonder if this is an SQLite database update problem, with Radarbox waiting for writes to complete to the SQLite journal, for example.
As an experiment, it might be worth backing up your navdata and mylog databases, and restart Radarbox with empty databases and see if the problem still occurs.