Several communities I have tried to join from this account appear to sit at SUBSCRIBE PENDING forever, but when subscribing to the same group from my Friendica account seem to sit in WAITING FOR APPROVAL for ~1 minute.
In both cases I appear to be able to interact with the community without any difficulty.
Subscribe pending will happen if the remote instance was unable to acknowledge the subscription request, either because of an outage or the server was overloaded. It won’t really matter on your end, you’ll still be subscribed and see the community in your subscription list. It’s probably going to affect how many subscribers the original instance sees for that community.