JunctionConnectionPool errors in pdweb.snoop trace file

Answer

TAM 6.1.1 introduces the feature of using persistent connections to
backend junction servers...

This can be enabled globally, and/or set for individual junctions.
The global settings are under the [junction] stanza, commented out by default (hence, disabling use of persistent connections to backend junction servers):

# max-cached-persistent-connections = 0

Even though the feature is disabled, the code which makes use of the
feature is still there... and while it would not actually try to add
connections to the connection pool (since it is disabled), the check
for an existing connection would still occur, and since no connections
would be in the connection pool, the following would be thrown:

Failed to find an existing connection in the pool!

and, with the feature disabled, it will not be able to add a used
connection to the pool, so you would also see:

Failed to add a new connection in the pool!

So if the backend persistent connections are not enabled, then these messages are normal and can be safely ignored.

With persistent connections enabled, there are valid reasons
that both of the errors could still occur... i.e. there could be no
connections in the pool, or none that are not busy, and you would still
see the first error... and if the pool is full, or the connection just
used could not be added to the pool (there are several possible reasons
for that), you would still see the second error.