I know it's a late reply to your question, but I recently encountered the same problem with a clients S55XM Hyster with a GM 3.0L lpg engine.
Turns out the engines had a problem with braking the starter pinion or even the nose cone of the starter when the engine fired immediately when the operator began cranking over the engine, so they incorporated a start delay electronic module just to the left of the battery, it would randomly fail and then start working again,, we removed it and installed a 12 volt DC delay timer we purchased for around $25 bucks from Fact#rymation, set it for about a 3 to 5 second delay & have hade no problems since... Much cheaper than the $1000.00 OEM
Hope this helps someone somewhere....