On Azure when drop vmsize or location field from cpms's providerSpec, a master will be in a creating/deleting loop.

4.12.0-0.nightly-2022-10-25-210451

always

1. Create an Azure cluster with a CPMS
2. Activate the CPMS
3. Drop the vmsize field from the providerSpec

New machine is created, deleted, created, deleted ...
$ oc get machine         
NAME                                    PHASE      TYPE              REGION   ZONE   AGE
zhsuncpms1-7svhz-master-0               Running    Standard_D8s_v3   eastus   2      3h21m
zhsuncpms1-7svhz-master-1               Running    Standard_D8s_v3   eastus   3      3h21m
zhsuncpms1-7svhz-master-2               Running    Standard_D8s_v3   eastus   1      3h21m
zhsuncpms1-7svhz-master-l489k-0         Deleting                                     0s
zhsuncpms1-7svhz-worker-eastus1-6vsl4   Running    Standard_D4s_v3   eastus   1      3h16m
zhsuncpms1-7svhz-worker-eastus2-dpvp9   Running    Standard_D4s_v3   eastus   2      3h16m
zhsuncpms1-7svhz-worker-eastus3-sg7dx   Running    Standard_D4s_v3   eastus   3      19m
$ oc get machine  
NAME                                    PHASE     TYPE              REGION   ZONE   AGE
zhsuncpms1-7svhz-master-0               Running   Standard_D8s_v3   eastus   2      3h26m
zhsuncpms1-7svhz-master-1               Running   Standard_D8s_v3   eastus   3      3h26m
zhsuncpms1-7svhz-master-2               Running   Standard_D8s_v3   eastus   1      3h26m
zhsuncpms1-7svhz-master-wmnfq-0                                                     1s
zhsuncpms1-7svhz-worker-eastus1-6vsl4   Running   Standard_D4s_v3   eastus   1      3h21m
zhsuncpms1-7svhz-worker-eastus2-dpvp9   Running   Standard_D4s_v3   eastus   2      3h21m
zhsuncpms1-7svhz-worker-eastus3-sg7dx   Running   Standard_D4s_v3   eastus   3      24m

$ oc get controlplanemachineset   
NAME      DESIRED   CURRENT   READY   UPDATED   UNAVAILABLE   STATE    AGE
cluster   3         4         3                               Active   25m
$ oc get co control-plane-machine-set      
NAME                        VERSION                              AVAILABLE   PROGRESSING   DEGRADED   SINCE   MESSAGE
control-plane-machine-set   4.12.0-0.nightly-2022-10-25-210451   True        True          False      4h38m   Observed 3 replica(s) in need of update

Errors are logged and no machine is created or new machine could be created successful.

Drop vmSize, we can create new machine, seems default value is Standard_D4s_v3, but don't allow update.
$ oc get machine                
NAME                                      PHASE         TYPE              REGION   ZONE   AGE
zhsunazure11-cdbs8-master-0               Running       Standard_D8s_v3   eastus   2      4h7m
zhsunazure11-cdbs8-master-000             Provisioned   Standard_D4s_v3   eastus   2      48s
zhsunazure11-cdbs8-master-1               Running       Standard_D8s_v3   eastus   3      4h7m
zhsunazure11-cdbs8-master-2               Running       Standard_D8s_v3   eastus   1      4h7m
zhsunazure11-cdbs8-worker-eastus1-5v66l   Running       Standard_D4s_v3   eastus   1      4h1m
zhsunazure11-cdbs8-worker-eastus1-test    Running       Standard_D4s_v3   eastus   1      7m45s
zhsunazure11-cdbs8-worker-eastus2-hm9bm   Running       Standard_D4s_v3   eastus   2      4h1m
zhsunazure11-cdbs8-worker-eastus3-7j9kf   Running       Standard_D4s_v3   eastus   3      4h1m

$ oc edit machineset zhsuncpms1-7svhz-worker-eastus3         
error: machinesets.machine.openshift.io "zhsuncpms1-7svhz-worker-eastus3" could not be patched: admission webhook "validation.machineset.machine.openshift.io" denied the request: providerSpec.vmSize: Required value: vmSize should be set to one of the supported Azure VM sizes