D01 Controller reported pilots on the ZOMBZ STAR to APA Airport are commonly making the mistake of missing the altitude restriction at FIRPI after crossing XBEEE and descending below the MVA and minimum published altitude for that segment of the approach.

Narrative

Aircraft X descending via the ZOMBZ STAR to APA and was cleared for the RNAV 35R approach at the XBEEE transition. The aircraft are supposed to cross XBEEE at 9000; then FIRPI at 9000; then JIDOG at 8000. Aircraft X crossed XBEEE correctly then started a descent to 8000 prior to FIRPI; causing them to descend below the MVA and minimum published altitude for that segment of the approach. I issued a low altitude alert and an immediate climb to 9000 several times as I got no response from the pilot. Finally the aircraft responded and climbed; eventually reaching 9500 where I then re-cleared them for the RNAV.This is a common mistake that pilots make on this STAR to APA. I have filed several other reports on this issue and it is still a problem. For whatever reason; pilots; after crossing XBEEE at 9000; seem to miss the additional 9000 restriction at FIRPI which protects for higher terrain south of APA.I don't know if it is an FMS issue or something with the approach chart that causes pilots to miss the FIRPI restriction when they brief the approach; but I strongly recommend that this issue be investigated to determine the cause. It's bad enough when it happens in VMC; but today it was IMC. It's terribly unsafe to be both operating below published guidance close to terrain and then making abrupt maneuvers to correct all while having no visual reference outside the aircraft.