Resently I had the same issue that PLM and VSL were not working. I noticed that this was only after starting from Cold and Dark. After playing a bit with this furthermore I have noticed that this happend when the INS allignment did not finished with Jester. So e.g. if I started letting Jester do the INS allignment, but started TAXI before getting from Jester the 'Ready to TAXI' then it did not work. But when waiting finishing the INS till getting 'Ready to TAXI' from jester then PLM and VLS are working fine. (not sure if jester is then not finishing something when it is not getting allignment complete?).
But this was my solution so far.......would be cool to hear if this is working for someone else....