In a realm and a bonemeal farm i recently built stopped functioning.
Link to the youtube tutorial: Minecraft Bedrock: NEW Moss Farm Tutorial! Easy Bonemeal Farm! MCPE Xbox PS5 PC (youtube.com)

Can confirm this functioned and produced about 9 stacks of EXCESS bonemeal in addition to what was fed back into the farm.  it was built and ceased functioning in the last 48 hours and is chunk aligned.

The behavior was that instead of the vast majority of stone becoming moss, nothing was. occasionally, only the back corners were converted. 

I tore out the stone and let it refill, no effect. I emptied, picked up, replaced and refilled the dispenser, no effect.

The only thing I can think of was while the farm was running I tried a gravity block duplication glitch with drip leaves which bugged out and stopped working after 2-3 reloads so I tore it down. 

was definitely in the loaded chunk range when i did it but didn't foresee this being a consequence.