You sir are my hero!
"somewhere else" is the key and I'm embarassed that I spent hours on this error.
I noticed that I pasted the wrong find command which is related to a different set of files I try to process.
The files from which I get the string starting with 00 are found by another find command for which I forgot to change the "old" call of capture() to capture2().
As said before I switched because of the sporadic ssh connection loss (which is out of scope for this "undef" issue).
But then I forgot that there is a second find/awk command with an additionally condition that works on a subset of files (containing the 00) that "coincidentally" get processed by an additional call of capture() which I forgot to change to capture2().
Basically the string $edr is empty because capture() is returning an array which I afterwards try to fill with a split on an empty $edr.
It's always the simplest error that soaks up the most time for troubleshooting :-)