PA18 Supercub pilot reported runway excursion on landing resulted from loss of control on landing.

Narrative

This event occurred in a PA18 Supercub during a solo approach to landing on Runway XX at ZZZ. Wind was variable at approximately 5 knots. ZZZ is notorious for quickly changing wind patterns and mechanical turbulence from nearby trees. That said. I was not scared of landing this airplane nor was I overconfident. I trusted my training and my skills to execute a safe landing; especially because I had previously conducted safe landings with 10+ knots of direct crosswind. My first approach to landing resulted in a full forward slip on final and felt unstable; so I executed a go-around from the roundout phase. Specifically; I felt that the tailwheel was not straight due to my forward slip.My second approach felt more stable and normal; so I continued to land. Roundout; flare; and touchdown all seemed normal compared to previous landings. I landed with adequate crosswind correction for the light left crosswind as indicated by a nearby flag. About 1 second later; the nose of the aircraft was pointed towards the right side of the runway and quickly veering that way. I did not execute another go-around for fear of aggravating the aircraft. Attempts to straighten the aircraft's direction were unsuccessful and the aircraft started to ground loop as it entered the grass next to the runway. The terrain next to the runway is downsloping; sandy; and it had rained for two days prior. These conditions exacerbated the ground loop when the main tire got stuck in the sand/mud and became the pivot point for a tight ground loop. The tail swung all the way around so that the nose of the aircraft was pointed at the runway. I then shut down; exited the aircraft; and called my employer for advice on further action.I was not injured; no other persons were injured; and there was no damage to ZZZ airport property. A&Ps will be brought to ZZZ to professionally inspect the aircraft and assess airworthiness/maintenance required.