Same here. It happened when I deleted a few testers from my External testers group. It suddenly expired all my builds from all my apps In appstoreconnect !? And it's not possible to add a new build and TestFlight builds stopped working. It's crazy.
{
"errors" : [ {
"id" : "ec667d77-523a-4f49-99dd-69e35d6870df",
"status" : "422",
"code" : "ENTITY_UNPROCESSABLE.BETA_CONTRACT_MISSING",
"title" : "Beta contract is missing for the app.",
"detail" : "Beta Contract is missing."
} ]
}