Are you maybe clicking on a layer mask icon in the Layers panel?
Nope. I did have some layer masks, but they were inside layer groups that were closed and not visible.
I'm not sure what you might be doing, but I haven't heard a lot of complaints here on the forum about Photoshop selecting alternate channels on its own... Is is possible you're fat-fingering a key on the keyboard just before this happens?
I'm scouring my memory and I can't think of a time when I've had a channel made active without being able to explain it...
I can only encourage you to watch for it to happen then very carefully review what you've just done.
Next time it happens, before changing anything consider doing a screen grab and posting it here. Maybe there's some other clue there that one of us on the forum might be able to spot. Maybe something will be showing in the History panel that will make it clearer...
I am getting the same exact issue.
I very carefully select my layer and go to move it using the cursor, and get this error.
I look in the channels panel and RGB is no longer selected only the Alpha channel.
I edit text, save changes, go to move the layer and get this error.
This is the first time this has happened to me as a photoshop user of 10 years. I am on Creative cloud cc and just updated photoshop a few days ago..
The only fix I know of is to select the alpha channel and delete it..
I had the same problem and found the solution:
Your top panel, go to Select then in the dropdown menu uncheck "Edit in quick mask mode". Then it switches back to automatic RGB channel selection from automatic Alpha selection.