Yes, I have owned many fine airguns. I would say more than half had reg creep issues. The object of my ire now, is not an expensive airgun, but the lowly Artemis P15 in .25. From the day I bought it, it was nothing but trouble. It came to me leaking air out of the box, accuracy was terrible (1 1/2-2" groups at 25 yards). Before the gun arrived, I ordered an Air-fective shroud with Venom moderator, and numerous other accessories-I never go in half way. I fixed the leak, but the accuracy was still bad so I bought a Huma reg with power plenum, and had Lee at Lee AirPro cut a Lothar Walther poly barrel. The accuracy was much better but it still took 3-4 shots for the gun to go close to POA after sitting even overnight.
As my wife never lets me forget, I put so much $$ into this gun, that I am considering parting it out just to recoup part of my $$. I would never sell anyone a gun that shoots like it does now. When I shot it today, it had an ES of 82, and an SD of 18 after putting the Huma reg back in. I am sure that with some tuning, I can make it better, but with the reg creep issue I will still not be happy. I have the Air Fective shroud (with barrel inserts) and Venom moderator, 3 Carm magazines, a Carm SS tray, Biathlon cocking lever, cheek piece, barrel picatinny sections, and adjustable butt pad all printed by Jake Bowman. In addition to the stock reg, I have tried the Huma power plenum, and have an Altaros on the way tied up in delivery. I can take this gun apart in my sleep, but I am about to throw the towel in on this one.
I do have P15's in .22 and .177 which never leaked, and shoot relatively well for guns with a base price of $550. For example, when shooting the .22 today, it had an ES of 14 and an SD of 4.4, and the .177 had an ES of 20 and SD of 6.5, which to me were acceptable, since neither of the two are really broken in yet. I heard that the P15 in .25 was the most problematic, and in my case, it sure was true, and I'm not sure any amount of money can make it what I want it to be.
I will be looking for that gun (preferably a .25) that I can leave by the back door and have it shoot where I left it when somethings shows that needs shot.