Field is not getting unlocked if I remove Auto number functionality from attribute

Hi,

In D365 MSCRM(9.0 online) , I set auto number formatting on single line of attribute using XRM toolbox. 

Later on, we decided to remove auto number field from that field. So from XRM tool box, I removed that formatting and observed, Auto numbering got stopped but that field is still locked.

After that, I checked customization.xml and found input mask for that field which was showing ReadOnlyOnUI.

Below is correct display mask for this field

<DisplayMask>ReadOnlyInUI|ValidForAdvancedFind|ValidForForm|ValidForGrid</DisplayMask>

I removed ReadOnlyInUI from that display mask and imported that solution again. But behavior is still same. I cannot edit that field as it is still locked.

Any idea on how to make this field editable after removing auto number on any attribute.

Thanks in Advance.