A broken feature on the mobile version nudges towards app installation, a broken feature on the desktop version does not.

This means that there is some benefit for Facebook to not fix the mobile version.

If a bug persists and benefits the company, we should - by principle - never assume it to be a bug.

We see the same right now with reddit, where old interfaces slowly (and clearly intentionally) crumble away, permanently signalling to the user that it is time to switch to one of the interfaces with a higher ad density.