Opensearch master user ARN always blank in console

When editing the security configuration for an opensearch domain to set the IAM ARN as master user, the "IAM ARN" input box is always blank even if you have previously saved a value. Thus, it is impossible to tell what the current value is. This comes up as I have observed open search seeming to "forget" the value that was entered here (possibly after upgrades?). When this happens, the IAM user that I have previously configured as the master user gets a 403 when attempting to access the opensearch domain. To correct the issue, I have to paste the ARN for this user back into this (always blank) field in the console and hit save. After the configuration is re-applied access to my user is restored. So really two issues here that may or may not be related. 1) Why is this input field always blank? 2) Why does AWS / opensearch periodically seem to lose this value forcing me to re-apply it?