wait why would your server get banned?
is it some kind of rule or something?
probably just a connection problem.. its no biggie buddy
try naming them.. so they wont despawn, if u name something it doesnt despawn i think
if it doesnt work.. then oof
i think i have a solution but it needs atleast 1 player on the server.. just 1.. its ok if its afk forever or something but it needs to have 1 player
give yourself a command block
place it then type inside the command block "/setidletimeout 100"
then change the command block to repeat and always active
so it'll repeat the command forever, making it online forever if it has 1 player..
if it doesnt work, try it on another time.. it worked for me in 1.14 servers but not above 1.14
hope this works!