On which field type are you using [Required] validation attribute? Or is this related to this issue. Can you please confirm that you are not following the steps similar to this issue?

https://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2019/6/validation-of-property-with-emailaddressattribute-fails-on-empty-value

Its string type, this issue is not related to the link you have provided. In earlier version, when the user filled with valid data in the property field, the required error message will automatically vanish. But after upgrading the Episerver to 11.4, this issue is happenning. The error message is still there in the page even having the valid property value. On clicking the error icon, it is vanishing.

Then, in that case untill you click on error icon, is your auto save is woring? (can you see there saving message appears)

Then, autosave with updated time.

Page is not saving

I am getting a warning message in browser console, "OBSOLETE: epi/shell/_StatefulGetterSetterMixin Use dojo/Stateful custom setters/getters instead".

Does this issue is causing by dojo.js?

Have you done any cusomization using dojo (in your project)?

Check this out, a related forum thread. This will help you

https://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2018/6/widget-on-modelchange-epi-version-10-vs-epi-version-11/