Ah. And it didn’t occur to you that people would need example data that shows all the possible scenarios to be able to solve your problem? :-)

Is the relay= bit always the last part of the line? In that case you could just use

m{ relay= \[? (.*) \]? }msx
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If not, then it is probably followed by a comma or end of line (again, can’t know without more sample data), so what you need is

m{ relay= \[? (.*?) \]? (:? \Z | , ) }msx
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Note that while I’m using a lazy quantifier in the second case (which is what is causing the problems in your patterns), it is followed by a non-optional part of the regex, so it will always be forced to consume as much as necessary to make the overall pattern match.

Makeshifts last the longest.