BUG #15815: Upgraded from 9.6.8 > 9.6.12 on AWS Aurora: SELECTs causing segmentation fault

The following bug has been logged on the website:

Bug reference: 15815
Logged by: Steve I
Email address: postgres-ca(at)byerquest(dot)com
PostgreSQL version: 9.6.12
Operating system: Amazon Aurora
Description:

AWS Aurora, stable on 9.6.6/8 for a year, updated to 9.6.12:

LOG: server process (PID 31294) was terminated by signal 11: Segmentation
fault
DETAIL: Failed process was running:
simplied >>> SELECT value FROM {table} WHERE lower(substring(value,1,1000))
>= '{string}'
LOG: terminating any other active server processes
FATAL: Can't handle storage runtime process crash

This specific SQL will cause a segfault on our dataset 100%. If I change any
part of it it won't e.g. remove lower, or substring, or change > to <, or
any part of the string. We have a few other variations, but this example is
the most often reported and reproducible.

Guidance on if this is a know issue, how to provide additional information
to further trace it in an AWS environment, or how to bypass it, is most
appreciated.