SSD USB-internal boot voodoo magic?

[wowzer]

I have a SSD (ADATA) that I used to boot a MacBook. It was working just fine, until my daughter pushed the power button and held it down to turn it off. Now it won't boot-just the folder with the question mark...hang onto the voodoo strangeness:

I put a different SSD into the laptop and it worked just fine (10.13.6). When I put the 'bad' SSD into an external USB enclosure, I can see the drive (running 10.14.x). I can even use this external SSD to reboot from the laptop. When I reinstall the SSD back into the internal, I get the folder with the question mark.

Is there something that I should do to fix this?

Thanks