cmssw: RelVal 132.0: (PDF) Info file not found

Since CMSSW_14_0_X_2023-12-04-1100 RelVal 132.0 fails for all flavors/architectures:

----- Begin Fatal Exception 04-Dec-2023 16:45:52 CET-----------------------
An exception of category 'StdException' occurred while
   [0] Processing  Event run: 1 lumi: 1 event: 1 stream: 2
   [1] Running path 'simulation_step'
   [2] Calling method for module Pythia6GeneratorFilter/'generator'
Exception Message:
A std::exception was thrown.
Info file not found for PDF set ''
----- End Fatal Exception -------------------------------------------------

Indeed, the code tries to open files like /_0000.dat, /.info or even "" (empty string). This is the origin of one such call (extracted with strace -f -k`: https://gist.github.com/iarspider/fdd17a07202e6ff4bb884f3751e37cd5

This seems to be a threading issue: running this relVal with single thread doesn’t generate an exception, while running with 2+ threads does.