It's the recent app update, looks like it's affected a lot of users.
I too shall try out this Metal in replacement for the app.
The app frankly is **** - it's just got more bloated over the years in terms of sizing. It took the facebook developers an absolute age to give it the feature of allowing it to be moved onto external storage - and even then the internal size is still a whopper.
It's CPU and Memory consumption are very heavy handed - i appreciate some people want news feeds loading extra quick, but i'd rather my phone run smoother/lighter and have to load the news feed every time i load the app.
It's the amount of extra data it caches that annoys me. Right now on my OP3 it's holding 161Mb data and 300Mb cache. I don't have any storage issues, but it still winds me up.
It's not just the Android version either, iOS was exactly the same.