When I was informed on such issue, I stopped them from any work on the variable frequency drive but ask them to check into the position of synchronizing encoder. I explain to them that the variable frequency drive 2 might have no output if the synchronizing encoder indicates that the section of roller chains driven by motor 2 are tight. The check was carried out and proven right. The synchronizing encoder was fully retracted because the sections of rollers chains for "cooling" was tight.
I ask the team to check on any obvious mechanical jam, especially by the ends of all loops because a straight run of chain normally should not jam. The team finally reported thaty there was no obvious jam and they are running out of idea on how to check further.