1911's have terrible gas capacity. TMs are the best 1911 because of the low weight plastic slide, but even TMs struggle to fire more than a single loads worth of bb's.
It's likely you will need to lube the slide as TMs can be quite dry out of the box. A dry slide will also increase gas usage to persuade a dry slide to move.
Also if you are constantly firing it in a short amount of time, the mags and gas get very cold, which means it gets far weaker and prevent the slide from locking back. The warmer the mags, the higher power the gas inside is.
TMs do not have silent fill valves so gas does escape when filling. This is perfectly normal.
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Lube the slide with silicon oil, don't constantly use 1911 gas pistols with rapid fire and I am sure it will lock back on empty every time.
Readjust your expectations, 1911s are cool, but the small gas capacity has always been a problem and you will need to regas for every load of bb's you fire.