With that being said, while Kinesis' own firmware for their keyboards (SmartSet) has gotten a lot better over the years, it still doesn't really come close to ZMK or QMK. To me the functionality of the firmware trumps the occasional reliability issues of the bluetooth.
I just hate that they pushed all customization to a third party. I got another set of blank PCBs for my Kinesis Advantage 2 by emailing Kinesis support (which is fantastic, by the way) and paying roughly 100 bucks for them. Now they send you to upgradekeyboards who are expensive and have massive lead times when I just want some PCBs so I can replace the gateron browns in my keyboard without having to desolder everything.
But if the connectivity issues are indeed caused by this, the only real solution is a new hardware revision.
I cannot overstate how much better having shift keys on thumb cluster is.
I got a Kinesis Advantage 360 through Upgrade Keyboards: https://upgradekeyboards.com/collections/kinesis-advantage36... with Box White switches, and it's been great. Expensive, yes, but great. I got the wired version for the usual reasons ("he who knows wireless, chooses wired"). YMMV. I also like the brown switches but like speed switches or box whites better.