Guys, you really need to add some bots! You've been trying hard to accommodate players by adding scheduled playtimes and Discord pinging for multiplayer, but you're fighting a losing battle as it still won't build enough of a user base for a consistent player presence.
If you add bots, it gives people an immediate opportunity to try out the main game rather than being stuck with target practice or waiting in lobbies. Once they experience the actual game in the cool maps fighting bots, they'll get invested and want to play multiplayer against real people.
Also, if you add bots, people will stay in your game doing that rather than leaving after training, which will automatically build a player pool for the online multiplayer, it's win-win!
I gave you 5 stars because the gunplay is solid (based on the training) and I want you to succeed!