On a dedicated server the player slots cannot be entered at least by admin almost on every try.

When that happens on client side of server admin there is the message "Packets acknowledged in an incorrect order" in the .rpt file. Testing showed that this message is created when the #missions command is executed.

This issue happens regardless if the admin Arma3 client is on same machine as the dedicated server or not.

When verifySignatures is set to 0 in the server config this problem goes away.

This problem originally occured with mods activated, but also happens the same with vanilla Arma 3. Changing SteamProtocolMaxDataSize to under, equal or over 1024 makes no difference.

The problem also occurred during Arma 2.08, but usually a restart of Arma3 client would resolve the issue.

When reverting back server and client to 2.08 this issue could be reproduced in the same infrequent manner with Vanilla again.

One difference i noticed is that if SteamProtocolMaxDataSize was too low for all the signatures, then with Arma 2.08 there was the message "Skipping signatures due to overflow flag being set." in the .rpt of the admin client, while this message will not appear with Arma 2.10.