In regard to: [Networker] all sessions slow at some time during backup,...:

Actually, this is Fujitsu Networker, not EMC Networker. Although we will
migrate to the EMC one because FTS apparently stopped developing theirs.

Ah, Ok.

I have *not* run nsrck (or so) which is supposed to verify the metadata
as the manpage says this is done anyway when you restart the server,
which I did when enabling debug mode.

Some checking is done, yes, but I don't think the startup checks
are as thorough as the checks that you can force.  For example, before
any upgrade EMC recommends a thorough index check be run, which amounts
to

        nsrim -X
    nsrck -m
    nsrck -L6

I'm kind of skeptical that the issue has anything to do with the indexes,
but the procedure is easy to perform so it may be worth a try anyway.

Tim