I believe this is a lemmy.world issue
Memmy - An iOS client for Lemmy
If your signed up on lemmy.world you will see some congestion for some time slowing things down. They've had a massive population growth in the past few days, thanks to rexxit. Myself included.
They've been working really, really hard on keeping it run as smoothly as possible.
But a solution some have suggested is signing up on a different instance with a lower population. They do not have any migration tools in place as of yet though, so you will be making a new account on the second instance.
I’m also on lemmy.world, and also experiencing the same issues. May consider firing up a second account soon
For what it’s worth, I’m also testing and submitting feedback for mlem, and both apps were working better last week ish, and started having similar issues at the same time for me.