If memory serves that particular brown in recent manufacturing from Lego was known by the public over some time to have embrittlement issues, so probably not something you did to it, but something as of now that Lego has fixed on their end if you pick up that brown from a current set or from their stores.
You can submit a request on their website apparently
The old brown from the 90s had the same problem; I’ve broken several while dismantling old used LEGO and it sucks. A lot of them were used in the old, kickass Pirate ships.
Where is your God now!?
Box of shame or hall of Fame, you decide where to hang this bricks frame