@_CG_Thibaud, thanks for looking into this, however it is not just Scala vs Scala. While it always happens with Scala vs Scala, it sometimes happens with Scala vs Other.
For example, I just tried to submit the simplest bot in the UTTT bronze league. The bot just takes the last valid move (from the provided inputs) and plays that. It is only 5 lines of code different from the default Scala code stub. It should not reasonably time out. Here are the times when I get PONG in competition. None of them were Scala. (Because I didn't played against any Scala bots in Bronze).
Totals: 11 PONGs in 220 games
Python3 bots (PONG)
Java bots (PONG)