Hughes 5003 lifters

I have installed these on a 1972 340 engine. I have had an issue with the lifter retaining ring popping off after a brief run period. Two different lifters. I triple checked pushrod seating during lash setting and rotation before firing up on run in stand. Lifter preload has been set at 1 turn past zero lash. I found the retaining ring laying above the lifter. The push rod was in place. These lifters are very particular due to rocker angle. Anyone else see this. Thanks
Rob Gary