2 sessions, but 4 queries

[Transistor]

The error seems to be,

SQLNestedException: Cannot get a connection, 
pool error Timeout waiting for idle object

A web search for that error gives many results including some on this site. See here, for example:

Error database connection

Right at the top: Cannot get a connection, pool error Timeout waiting for idle object This isn't an error on the database side, strictly speaking. Ignition makes multiple internal connections to your DB and recycles them as each query completes. The number and behavior of this "connection pool" is part of the advance settings on a database connection. Not getting a connection for this timeout means you are running more simultaneous long queries than your DB can handle. Either your queries …