The mod Rampant, fixed (2.3.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RampantFixed::on_tick (ID 0)
LuaCommandable belongs to surface fulgora (index 6) but a LuaCommandable belonging to surface nauvis (index 1) was expected.
stack traceback:
[C]: in function 'add_member'
RampantFixed/libs/SquadCompression.lua:155: in function 'squadDecompress'
RampantFixed/libs/MapProcessor.lua:294: in function 'processPlayers'
RampantFixed/control.lua:1530: in function <RampantFixed/control.lua:1481>

was exploring on fulgora

This is, of course, an extremely strange situation, but I'll add a check in the code for this case.
The release is expected this weekend or Monday

I have nearly the same error by working on Vulcanus.

Error while running event RampantFixed::on_tick (ID 0)
LuaCommandable belongs to surface vulcanus (index 3) but a LuaCommandable belonging to surface nauvis (index 1) was expected.
stack traceback:
[C]: in function 'add_member'
RampantFixed/libs/SquadCompression.lua:155: in function 'squadDecompress'
RampantFixed/libs/MapProcessor.lua:294: in function 'processPlayers'
RampantFixed/control.lua:1530: in function <RampantFixed/control.lua:1481>

Yes, thanks to your two comments, I found the cause: it wasn't taken into account that a player could be in the same position as a squad, but on a different planet.