[AoA 2.4B] "Client Outdated" & Server stopping...

Hello , my brother and I played Advent of Ascension 2.4B on Minecraft 1.7.10 for a while now and after the Aternos page update, the new layout and other features, it still worked well, I like the waiting time reduction and the layout, but after a couple of days we wanted to start the server up again and play, we got nothing changed, not even our minecraft client options, waiting for server to start then all of a sudden it says "Server stopping...", yes I did confirm when the notification popped up, but after that it happened. We tried again, then after waiting it stops again, didn't even start the server, after waiting for it to start it stays offline and says "Server stopping...". We tried the next day hoping that it will resolve itself and the server started, it went online. But when we tried to connect to it (Like I said, nothing changed, we did everything like before), it says "Outdated Client...". It would be a disappointment to start AoA surviving from the beginning, we accomplished to much in our world and would like to continue, which has nothing to do with the topic here, but I would still like to know of a way to resolve the issue and make the server work again. Thanks in advance.

Thanks!