I had a similar issue, but the value that should have been updated was null. It was because instances of my class overridden my default value and set it to null. To fix this issue in the property(value) which should be updated in UMG add this
UPROPERTY(NonPIEDuplicateTransient)
int32 MyValue;
As I understand it will keep default data from the default class.
Who wants to read more about it Property Specifiers