I’ve had exactly these problems, with Furutech. I’m sorry, Furutech kind of sucks in general for bananas. I’ve also found them super easy to deform.
WBT’s bananas are slightly tighter fitting, and if you can avoid Rhodium you’ll have a better connection. Rhodium is beautiful and far too hard. Gold plated is going to be a better long term connection. If you used the copper crimping sleeves, you'll find they slip right on.
Another alternative is the WBT spades. The built in spring loading makes them keep good contact even with very hard plugs like nickel plated.
