I just want to mention that a while back I reported a bug where I would get iOS notifications about ruins invites from members, but the ingame private chat window would be missing most or all of them if the game is already running in the background. I posted proof screenshots to support a few weeks ago and got confirmation, but I am not sure if anything was done about it.
That's not quite correct. As far as my experience goes, the notifications about the invites while the game is running in the backgroud still can be displayed. Try to force the chat to reload by either restarting the game or switching to guild or global channel.
I still get days where I send out 10+ invites and accept 10+ peoples' invites, but they don't return the favor. Either my members are super negligent, or the system is still broken and they just don't see them.
I wouldn't call the negligent. See it from the other side. You're helping 10+ people everyday, but only receive a reward on time per day. The other 9 times are "wasted". When I receive invites I'm doing a single one for the reward and from then I only help guildies whose ruin is about to run out of time, giving the rest of the guild the chance to get their daily reward as well. I also don't attack my own ruin.