I have NEVER experienced your "Previous Experience".
I had to restart RT EVERY time a monster interrupted, as I trained up from 30. Period. And I did 200-300 Stash-Cache maps in the process, and NEVER left the side of the chest. The ONLY difference was the "Lock Jams" message with the Hoard and Trove, which appeared to be color text, as I never experienced an automatic restart of RT, ever, with ANY level of chest at ANY level of RT.
Very, very strange... I went from 28 (bought from thief NPC) to 75 skill in probably 25-30 supply maps. The only time I had to restart remove trap was my first map under the new process because I had to move a second account out of harms way from the constant explosions every 10 seconds doing 30ish damage each. All of the other maps would keep the process ticking, doing explosions every 10 seconds or so and spawning a blue guardian each explosion if there was not already one out. Never had two guardians at the same time even if it took more than 10 seconds to kill the existing one.
This was exactly how I understood the process was supposed to work based on the notes:
From UO.com wiki regarding remove trap:
“These give the best gains, but require a treasure map to be dug up. There is no minimum requirement for the different chest levels, instead the length of the process is variable based on the player’s Remove Trap skill, with higher Remove Trap skill requiring less disarming time. During the disarming process Ancient Chest Guardians, chosen from the monsters that can spawn during the initial dig, will spawn to defend the chest, accompanied by some fire damage to the digger and any nearby party members. These monsters will not drop any loot and must be defeated before the chest can be opened.
If the player moves more than 16 tiles away from the chest or is killed during the disarming process, the process must be restarted. The disarming process begins when a player uses Remove Trap on the chest.”
The same description is used on the treasure map potion of the wiki.