Edit: Wrong mod, my bad, error comes from this fork:
https://mods.factorio.com/mod/ccp-noooo

Error while running event ccp-noooo::on_init()
Error when running interface function automatic-underground-pipe-connectors.add_undergrounds: automatic-underground-pipe-connectors/control.lua:314: attempt to index local 'pipe_prototype' (a nil value)
stack traceback:
automatic-underground-pipe-connectors/control.lua:314: in function 'validate_lookup'
automatic-underground-pipe-connectors/control.lua:348: in function <automatic-underground-pipe-connectors/control.lua:346>
stack traceback:
[C]: in function 'call'
ccp-noooo/control.lua:84: in function 'add_automatic_underground_pipe_connector_support'
ccp-noooo/control.lua:93: in function <ccp-noooo/control.lua:88>

It looks like that fork removes the fluid color pipes, and this error is caused by the mod still assuming that the pipes exist. Because you have automatic underground pipe connectors mod enabled, during on_init the fork mod is trying to register the undergrounds with the automatic pipe connector interface, including the fluid color ones that have been removed, and automatic underground pipe connector mod is erroring trying to lookup a pipe that doesn't exist.
This is happening because the list of colors used in control.lua:76 still contains the fluid colors. The immediate fix for that would be to remove the fluid colors from the color list (constants.lua:113-121). I think that should work, but maybe there's something else I'm overlooking.

Thanks for the hint! I'll try the fix. I forwarded it to the fork author too.