Connection issues? Other players cannot break blocks

Hey, So recently I've started up the server and while I can connect fine and break blocks, when I have friends try to connect they couldnt break any blocks and I tried opping them to fix that, in which it didnt work. So then I tried resetting the server and now they cannot connect at all, saying that they "Cannot connect to server"

Well I dont know but I seemed to fix the issue now with the blocks and connection issue for a while. But now after I tried to put in the feed the beast direwolf20 modpack it now kicks all the players off the server after like 5 minutes

I know that, but my friends and I would be moving and they would kick us off the server and then we cannot reconnect. giving a "connection failure" or "the server is offline"

No, after we've been kicked we cant rejoin; and earlier when I tried to connect to the server to see if I could join but I couldn't join at all, giving me the same messages from before.