After some sleep, I tried some more boot cycles with Bonsai and kernal 38.8-bfs. Maybe half the time it works as it should and half the time it reboots. Tried to determine if I'm doing something different during the successful cycles but can't isolate a reason.
Installed kernel 18.104.22.168-pclos1.bfs. No problem with install. No problem with shutdown after 4 cycles. I think the 33.7-bfs from last year's Bonsai as well as this 37.4-bfs will have no problems reguarding shutdown/reboot. I want to keep this kernel for a day or two for more testing. Then, if you think it will help, I will try the 38.8-non-bfs (it did not work reliably in my OB full test install).
Just some info about installing this kernal, as I said I had no problems this time and I had no problems yesterday installing different kernel to my OB full. During the synaptic install it did get to a point where it stopped for maybe 1 minute, but then it continued without problems. Today after this 37.4 install I have different grub entries from what I got yesterday installing the 38.8. (Maybe there are different install scripts in each kernel package?) Anyway, now I have my original grub entry, which points to /boot/initrd.img, which is a symlink to the last installed kernel. And I also have two new grub entries, each pointing directly to it's respective initrd file in /boot. So I guess I can now boot whichever kernal I want.