If it won’t go above 500 PSI even with the compensator spring fully compressed, I’d start looking somewhere other than the adjustment itself. Could be an internal leak, a relief valve stuck open, or the pump just isn’t building pressure anymore even though everything looks good visually. I’d also check the suction side for any restriction or air getting in. Since it happened suddenly, I’d suspect a valve or seal failed somewhere rather than the adjustment getting out of spec.