If a community appears as a 404 page when you click it, it likely means that the community is being hosted outside of the instance you are currently using and that nobody in your instance has viewed or interacted with that specific community yet. In order to address this, you will need to copy-paste the specific handle for the community (for example, !tampabaylightning@lemmy.world) into your searchbar so that your instance can "learn" that it exists, after which the community should display via linked URLs without issue. Hopefully this is addressed by the lemmy devs and streamlined in the near future.
Gah, this is the kind of thing that kills adoption. I can browse to the Caps community on https://lemmy.world, no problem. I see other lemmy.world communities on lemm.ee that I'm using and subscribed to. But I cannot get caps@lemmy.world to show up in the app or in search on the website. I tried another team community (I forget which) and had the same experience. But I've been able to add other lemmy.world communities to my subscriptions, and I know they work. Lemmy.world is listed as linked on lemm.ee, and vice versa. Basically everything says it should be working, but it isn't, so it's probably just some temporary issue.
I know once the server 'finds' it the first time, it should work fine, but right now it's just frustrating - and I'm pretty patient.
Just added them! I suspect the sub pending may have something to do with the lemmy.ml servers being crushed right now, as I haven't run into that until today.