I have not systematically kept track of it, so I am afraid I cannot provide detailed information for your questions.
Altogether, I would not rate the issue as "frequent" but instead rather as "now and then". I have not systematically attempted to recreate it. Since VASSAL v3.2.17 is the current version of VASSAL for quite some time, my *guess* is, that it does likely happen with this version being present on both sides.
As for the VASL version, I have been using v6.4.2 only since the beginning of this year and v6.3.3 before it. As far as I remember, I had it come up in various versions of VASL.
I *think* to remember, that when the problem came up, both players were affected.
All the best,
von Marwitz