Roland Promars LFO glitch

Hello all, nice to be here!
I have a Promars which I love to bits but it has an intermittent fault where the LFO seems to kick in and shoot up to a ridiculous speed and for a few moments the synth is unusable. It then gets over itself and is fine again. Sometimes it can last a few minutes, sometimes it might go for 2 or 3 hours without glitching at all!
It can do it if it’s just sitting there, or if I’m in the middle of playing, it’s completely random. No slider, knob or keypress seems to specifically make it happen.
Just wondering if this is anything anyone else has encountered and if I can find the cause! When it works, which is most of the time, it is fantastic!
Many thanks in advance for any ideas or advice!