If there are no clients connected, the fastest way to get to a working stack is likely to factory reset the switches and build the stack again following exactly the instructions (like when to switch on the switches).
I had the same issue when setting up my switch stacks. To resolve, I had to shutdown all of the switches in my stack until the status messaged changed to down or not connected. Give it a good 10 minutes and the dashboard should switch to that message. After that message shows up, power on all switches in the stack and it should come back up without an issue and connected successfully.
We just replaced 3 switch stacks about 4 months ago and I figured this issue out early on 😁 If your maintenance window allows you to wait, I agree with @alemabrahao and @PhilipDAth. If you don't (like we didn't) the power cycle and wait will do the trick.