Error saving staff details into SharePoint List

Hi,

We currently facing some issue saving person details into SharePoint list.

We have an existing PowerApps forms which serve as an online application form. Once the form has been submitted, the data will save into SharePoint List and an approval workflow will kick-off. The form has been working fine since last year until recently we noticed that it stop working. We are having this error - An entry is required or has an invalid value. Please correct and try again. This is an error on the person mandatory fields in PowerApps, even though the staff profile has been selected from a ComboBox selection list. SharePoint does not seem to register this selection and return the error and no new item is created. 

We are having the same issue with another case where instead of PowerApps, Microsoft Forms is used to collect data and save into SharePoint List. 

Has anything been changed recently? Wonder is there someone else facing the same issue and any fix for this?

Thanks