It seems that he either died of old age (he was 7 months old and already had wings so had his last moult) or that one of the roaches he consumed might've been not 100% healthy. He got really lethargic and struggled to walk or hold up his head properly, so I tried feeding him honey as the internet said it may help, but unfortunately he just gradually got worse until he wasn't mobile any more.
Rest in peace you magnificent creature