Anyone have this happen?

I've got Artillery everywhere and last night, more than once and from different locations, I get the message to stand back the shells are coming ... and nothing happens. Then about a minute later they say that's all and to clean up the rest myself.

The settlements are in good standing. No "!" on their names. Artillery are manned (I went there to check). Just no shells are falling.

Has anyone had this happen? Is it a known bug? Is there a way to fix it? If Hancock does Jet does he still have to pee in the morning? Inquiring minds want to know.

Thanks.