Only happened once and can't verify for sure that this was the cause...
Forest Colony Map. I was out in the water, at the broken Dropship. I was piloting a Raven 3L and running ECM in Counter mode I believe. Got stuck on some of the debris located against the dropship. Nothing would work to get me unstuck...hit X to come to complete stop, and then tried moving out...no good. I happened to switch from Counter Mode to Disrupt Mode to try to stop me from being targeted and as soon as I did that, my mech because Unstuck and I was able to continue.
Can't say for sure that was the cause or solution, but just throwing it out for consideration.