Are they solved? I still see a lot of reports of people with issues with ZMK 3 on the 360 Pro. Someone who does switch replacements for the KA2/360 said that there is a design error in the 360 Pro, where on one of the halves the key well flex cable runs through the Bluetooth antenna clearance area. This also explains the high variance: how much the issue affects you depends on how the flex cable happens to be oriented in your unit.
But if the connectivity issues are indeed caused by this, the only real solution is a new hardware revision.
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.