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

[Arjun Ranade <ranade@xxxxxxxxxxxxxxxxx>]

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