Ultra Compact Pro 45

I purchased my first Bersa 380 in 96 ish and have loved it ever since. I recently was lucky enough to find an Ultra compact pro 45 at a local gun store for a steal and just couldn't resist. I took it to the local range and the first 100 rounds were flawless. At about 120 rounds, the seventh round of the second consecutive magazine failed to feed and the slide would not return as is should causing an inability to fire. Easy fix was to manually push the slide in place allowing it to fire. Only time this occurred was the fourteenth round, last shot when two magazines were used back to back. Any ideas??????