I work for a company that teaches Java using Minecraft. We are located at 128 colleges in the US. We've purchased a full account (Minecraft.edu denied us) for each machine.

At our large locations where 50-100 students are logging in at one time (each with separate accounts/passwords), we're noticing that after the first 30-or-so log in, the rest are getting error messages that read: "Error! Unknown e-mail address or password." If we tether to a phone or try from our office, the account/password works fine. So it's something to do with the IP address, we think.

Accounts are being denied after a certain number of logins; but the next day they'll work.

Unfortunately, we can't split computers over multiple IPs as we're on college campuses and they're stingy.