Um, so why didn't you title your post:
"FlarmView choking on too many targets?"

I fly with 10-14 PowerFLARM-equipped gliders. Our club standardized on Butterfly displays early on, one or two private owners have FLARMview. We haven't seen this behaviour.

When I had a similar problem with my Butterfly about a year ago, it manifested only with specific unit settings (imperial units - kts, nm, ft), oriented vertically. You might try changing from whatever units you use to the other (metric), and change orientation, to help troubleshoot the problem. The more the data, the easier the fix. I also took a cellphone video of the problem, posted it to youtube, and sent the link in. It took Butterfly folks about a day to fix and produce a beta version for me.

The Butterfly is not as bright as flarmview, but the support is very good, and they're (the equipment, the factory support folks, and the Canadian dealer) easy to work with.

I'm curious how many of the gliders had transponders as well as PowerFLARMs - it seems to me that might double the I/O the processor has to deal with. Only one local glider has a transponder here...