pgrep doesn't find processes from other namespaces anymore
The commit dcb6914f ('Support running with child namespaces') changed defaults and made pgrep/pkill fail in cases in which they've worked. The author's argument for the change callers not expecting to break other namespaces should be pondered against callers expecting to work as it always did.
Changing defaults is not a good idea. I've always regretted :) Not to mention that, when the user has the right to kill a process, limiting pkill doesn't help much, because it can still be done with the kill command.
I suggest that the scripts/programs wanting the namespace contained behavior should correct their assumption and use
pkill --ns $$ and
pgrep --ns $$, making aliases, placing wrapper scripts in $PATH or be contained.