All airtags disconnected at once

Ok, there are a number of reasons your AirTag would beep. They are:

• The iPhone you paired it with is outside of the Bluetooth range (~30-40') of the tag after a certain period of time. Typically, that would be between 8 & 24 hrs. If you had this tag, along with the phone you paired it with, with you, then this shouldn't apply.
• If your tag's battery is low it will start beeping.
• You initiated the beep via the Find My app.
• You are setting up the tag.
• Someone else with an iPhone nearby, initiated the beep. This would happen if they got an alert that an AirTag is "following them." To help them locate it, they can send a signal to it to cause it to beep.

So, if none of these apply in this situation, it would be unusual for it to just beep ... but not impossible.

You also mention that all of your AirTags are "disconnected." Are you saying that none of them show up on the Find My app's Items tab on your iPhone?

How long have you had these tags? Did you have to replace their respective batteries? If so, did you make sure you used replacements that do not have a bitterant coating on them?