One: admin rights
Check first because it breaks most often and is invisible. Someone reorganises the admins, or the bot is re-added without its permissions, and everything it needs permission for silently stops. A bot can be in a group, look present and be able to do nothing.
Two: the group privacy setting
If moderation and analytics see nothing while commands still work, this is almost always it. Telegram withholds ordinary group messages from bots while privacy mode is on, and it is on by default. It is changed in BotFather by whoever created the bot.
Three: is the module on for that channel
Modules are per channel. A setting you turned on for one group is not on for the next one, and a new channel starts with nothing enabled. Open the channel in the dashboard rather than trusting your memory of a previous one.
Four: the token
A token revoked or regenerated in BotFather leaves your bot connected to nothing. If you rotated it for any reason, it has to be updated where you connected the bot.
Five: a plan limit
Limits are checked before an action rather than after, so being over one looks like a refusal and not a crash. Count the channels you manage, remembering that a storefront occupies a slot too.
Six: ask the bot directly
Send it a command in a private chat. A reply there means the bot and its token are fine and the problem is a permission or a setting in the chat you were testing. No reply means the problem is the bot itself, which narrows everything above to the token and the connection.