Can concurrent create index concurrently block each other?

One our customer complains that he spawned two `create index concurrently` for two different tables and both stuck in "waiting for old snapshots".
I wonder if two CIC can really block each other in `WaitForOlderSnapshots`?
I found the similar question in hacker archive:

https://www.postgresql.org/message-id/flat/MWHPR20MB1421AEC7CEC67B159AC188F6A19A0%40MWHPR20MB1421.namprd20.prod.outlook.com

but it is quite old (2016). Was the problem fixed since that time? And if not, why there it is not mentioned in CIC documentation that performing several CIC in parallel can cause "deadlock"?

Thanks in advance,
Konstantin