Strange behavior from cu on armv7

[bob prohaska]

Lately cu sessions (or something closely-related) have taken to
misbehaving on a Pi2 running -current.

The situation is:

ssh into armv7 host which has a pl2303 plugged into it
su to root
run cu -l cuaU0 -s 115200 to connect to the serial port of a Pi3 

Most of the time the connection behaves normally. The pl2303 is prone
to locking up over time, seemingly faster (an hour) when the armv7 host
is loaded. In that case, unplugging and replugging the pl2303 aborts
the cu connection, which can then be restarted and again behaves normally.

Lately, the unplug-replug cycle produces the normal recognition and 
allows the cu session to be restarted, but no data is tranferred.
A "connected" prompt comes back, but there's no echo and no data. 
Further unplug-replug attempts don't change anything. A reboot of
the armv7 host restores normal behavior. 

In a couple of cases unprintable characters displayed:

root at www:/home/bob # cu -l cuaU0 -s 11520oo}root at www:/home/bob # cu -l cuaU0 -s 115200
Connected
[hex characters didn't copy/paste]

FreeBSD/arm64 (www.zefox.org) (ttyu0)

login: �

FreeBSD/arm64 (www.zefox.org) (ttyu0)

login: 

And all is well, for now.

Thanks for reading, and any ideas.

bob prohaska