Got one of these as well, and periodically have the same issue.
You need to clean the lead-screw that operates the rise and fall, a job which unfortunately can only be done from below. Give the machine as good a vacuum out as you can before getting down there with a small brush and the vac to attack the threads. I would strongly advise eye protection and a mask as you're going to get showered with the dust you didn't get in stage 1. You'll need to clean the thread at both ends of travel and it helps to have a third hand to operate the mechanism while you clean it. Don't use any kind of wet lubricant on the thread once clean, it will attract dust and you'll be doing the job again much sooner than you'd like, use PTFE spray or a dry silicone lube if possible. WD40 does an ok job and helps clean out gunk from the travelling nut, but wipe off afterwards so you just leave the residue.
If you feel particularly he-man like you could carefully roll the saw onto a couple of 4x2s and do the job from the top, but this isn't really practical if you have the extension/sliding table(s) attached and nicely set up
