On both boards, the upload seemed to proceed ok, with five sets of "Sending frame" and "Got frame request" messages, ending with "Upload complete!" However, after the upload, neither board outputs anything (no logging and no help menu) to the USB serial monitor, nor do they log to the microSD. Experimenting with the host baud rate makes no difference- no characters, garbage or otherwise, appear.
A third OLA, which I didn't update, works fine, indicating, at least, that my USB host terminal setup (Arduino IDE Serial Monitor at 115,200 baud) isn't the issue. I close the Serial Monitor window, unplug all USB devices, connect an unhappy OLA to the PC (Windows makes a happy beep), and select that OLA in the Tools:Port menu. I then open the Serial Monitor, but can't get a peep out of the OLA.
Pressing the OLA's reset button doesn't help, nor does typing H or ctrl-x. Moving the microSD card from the working OLA to either of the unhappy OLAs doesn't help, either.
I called the unhappy OLAs "semi-bricked" because re-running the Firmware Uploader on those otherwise non-responsive OLAs yields the same series of "Sending frame," "Got frame request" and "Upload complete" messages, indicating that the host can communicate with the OLAs through USB just fine, at least with the Firmware Uploader.
The solution to this issue is probably something simple but, being new to the OLA, I don't yet know how to troubleshoot this. Can you suggest some things to check?