I had a vein problem develop from accidentally wearing a stretchy cock ring overnight. Pumping, wearing a cock ring or any prolonged (say over 5 minutes) constriction caused an almost BB-sized lump in the vein.
Depending on how badly I aggravated it, the lump (often not only one, but a series) would go away within a few hours to several days. I continued PEing and tried to avoid techniques that irritated it the most. I’d have to search my posts to figure out when this first happened - maybe 9 months ago? But now it’s no longer a problem. I have a different vein bothering me at the moment. :(
In my experience, pumping, wearing a cock ring and wrapping for girth are some of the worst things a guy can do when dealing with a thrombosed vein. Anything that hinders blood flow for many minutes is bad.
My suggestion is to take several days off all PE, then start back with a few minutes of easy jelqing (no pumping or cock rings). See how it goes. If the vein clots, take a longer break, maybe a week or two, then try lightly jelqing again. It’s a tough call how long to rest before trying again. Play it by ear.
>What I found is, it seems like the vessel became too long due to the stretch and then when getting flaccid, it creases so much that the blood won’t get through anymore.<
Something irritated the vein. Perhaps you can adjust your hand position to avoid overstressing it. If you wet jelq, you could try dry jelqing. Or switch your grip from underhand to overhand or vice versa.
If the clot is there immediately after your workout, the crease when you go totally flaccid isn’t the cause. OTOH, if it’s ok right after your workout but clots later, then the kinking may be contributing to it.