PG10 - Out of shared memory / invalid memory alloc request size

We recently upgraded a database that a number of developers use from
Postgres 9.4 to 10. Our memory parameters are unchanged.

We are seeing a lot of errors that look like this in the postgres log:

< 2017-11-14 13:13:59 EST [144172] : [1-1]
user=[unknown],db=qa16,remote=192.168.104.22(35238) > FATAL: no PostgreSQL
user name specified in startup packet
< 2017-11-14 13:52:22 EST [6273] : [1-1]
user=deployment_app,db=qa5,remote=192.168.104.83(45384) > ERROR: out of
shared memory
< 2017-11-14 14:17:53 EST [6200] : [3-1]
user=service_tracker_app,db=qa16,remote=192.168.104.22(46996) > ERROR:
invalid memory alloc request size 34359738368

Anecdotally it seems that these errors are happening when
powa_take_snapshot() (Postgres workload analyzer) is running as well but I
can't confirm that.

Does anyone know how to debug these types of errors? And once the db is in
this state, how do we resolve sessions reporting "Error: invalid memory
alloc request size" - killing the sessions and having them reconnect does
not fix the issue.

Thanks,
Arjun