For me, being stuck at ‘Subscribe Pending’ does seem to happen for KBIN mags, but it isn’t exclusive to them. Whenever it happens, it does the mad thing of bringing everything though up to the point I tried to subscribe, but nothing after.
To fix it, you can often - but not always - go to the source Mag or Community, and find a semi-recent post from after you subscribed, and copy the absolute link (e.g. kbin.social/…/Visualizing-the-mysterious-dance-Qu…), then go to your instance and post that in the Search field. And then the change the thing your searching for from ‘Communities’ to ‘Posts’, and then wait a bit, and then click the link if it shows up.
This tends to force through the change past ‘Pending’, and from then things will start turning up.