Too high a UBI might lead to inflation. In that case, if we've indexed UBI to observed or predicted inflation we could indeed wind up with a positive feedback

Too high a UBI might lead to inflation. In that case, if we've indexed UBI to observed or predicted inflation we could indeed wind up with a positive feedback loop and hyperinflation. So don't do that. Index to targeted inflation. If it's too high and we see more inflation than targeted, the UBI will fall in real terms. If inflation falls short of target, the real UBI will increase. Negative feedback loop - probably stability or oscillation.