prune the tracked validator cache before updating

beacon-chain/rpc/eth/validator/handlers.go

@@ -547,6 +547,8 @@ func (s *Server) PrepareBeaconProposer(w http.ResponseWriter, r *http.Request) {
 		httputil.HandleError(w, "Could not decode request body: "+err.Error(), http.StatusBadRequest)
 		return
 	}
+	// Prune the tracked validators
+	s.TrackedValidatorsCache.Prune()
 	var validatorIndices []primitives.ValidatorIndex
 	// filter for found fee recipients
 	for _, r := range jsonFeeRecipients {

beacon-chain/rpc/prysm/v1alpha1/validator/proposer.go

@@ -340,6 +340,9 @@ func (vs *Server) PrepareBeaconProposer(
 ) (*emptypb.Empty, error) {
 	var validatorIndices []primitives.ValidatorIndex
 
+	// Prune the tracked validators
+	vs.TrackedValidatorsCache.Prune()
+
 	for _, r := range request.Recipients {
 		recipient := hexutil.Encode(r.FeeRecipient)
 		if !common.IsHexAddress(recipient) {