You will get the posts in your feed, even though the sub is pending.
The pending thing happens when federation on that instance is overloaded. You'll have to come back later and unsub and resub to get the pending thing to go away.
You sometimes don't... Or they come in with a delay. Comments and votes are also going missing. It's a known issue with the bigger instances, outgoing federation gets bottle-necked and starts dropping stuff. v18 improves it massively but .world hasn't updated in waiting for v18.1
Not that I can tell. It might, if you're the first to sub, but aside from then, you still get anything that makes it to your server in your feed.
There could normally be some latency waiting on a server response, but you'll still get the feed even though it says pending. There is a problem where it can get stuck in a pending state, but I thought it was resolved in the recent 0.18.0 update for Lemmy. Though some admins are holding back until 0.18.1. Lemmy.ml has updated, but maybe both the local and remote instances need to have the new version. Kind of a bummer, I really want the fixes in 0.18.0, but I think the admin of my login instance is holding out for the 0.18.1 version.
They scraped captcha support in 0.18.0 and only opted to add it back in after massive instance admin protests. In the middle of a bot-wave, that was a major dick move. Captcha is not infallible, but it sure gets the majority of script kiddies out. The good thing is that the feature has already been (re-)developed and merged into the main app, so we know it's coming in 0.18.1, and that was the main dealbreaker for most instance admins.
I hope it has a short release cycle because 0.17.4 has some glaring bugs and I'm really hoping for some improvement. For example I'm getting missing posts which is kind of driving me batty. Then the sort orders don't work right which is also causing some angst. Though not to complain, I'm enjoying my time here and I'm willing to put up with some growing pains. It's just these issues are starting to get tiresome.