Today my X server on my client machine crashed for an unknown reason, and after that I was unable to reconnect to the X2go session that I had been trying to reconnect to at the time of the crash. Until, that is, I spotted an errant ssh process and killed it. After that, I could reconnect again.
Conclusion: x2goclient should always ensure that its child ssh processes will die as soon as it is killed.
If the git repo appears as promised, I might fix this myself.
Robin