Same here, kerning panel is empty.
on a test font I’ve deleted all the kerns (select all, cmd+cancel).
Below the kerns count did not change.
Also, closing a file did not flush the kern panel.
My panel is empty on opening Glyphs but switching applications (via Command-tab) repopulated the panel.
I’m on Version 2.6 (1192)
I have not experienced this a single once yet.
Does it also go away when you just click in the canvas or zoom?