I first reported a problem when using the Live View button here:
https://www.pentaxforums.com/forums/190-pentax-k-1/319873-post-k-1-bugs-issue...k-ricoh-3.html
I thought it was connected with the camera drive mode being in mirror lock-up, however I can confirm this is not the case as I did check and add some updates to the problem here:
https://www.pentaxforums.com/forums/190-pentax-k-1/319873-post-k-1-bugs-issue...k-ricoh-4.html and here:
https://www.pentaxforums.com/forums/190-pentax-k-1/319873-post-k-1-bugs-issue...k-ricoh-5.html
This morning I was in bracketing mode and there was more ambient light than normal, so when it occurred again I could see what looked like a bracket and I thought I'd take a photo of it as it appears on the screen in live view. Well, I would have if I'd remembered to take my phone with me.
So instead I left the camera on and removed the lens. With the camera on in LV the mirror was down. Thus my original suspicion is unfortunately correct.
The issue is intermittent, I can be turning LV on and off several times when I'm out and it might happen only once or twice in that time. As an estimate maybe 5% of the occassions I press the LV button the mirror will not raise.
I guess I get to send mine back to be sorted, but for now it has to wait.
Tas
Edit 25 May: No mirror silliness in live view this morning though I noticed that the normal sounds when actuating the shutter were much louder on two occassions. The image was captured in each case but that sound combined with the other issue now has me worried. Guess it will need to go in for a check up.