While working on Field Security Profiles, You may face issue.
Your user is created properly with proper role assigned to it.
Field is also marked as “fields security” as true.
And I am sure you have published all the customization at this point.
And still you get following issue.
The User does not have read permissions to a secured Field.
This issue is Because of caching.
Either Clear your cache and try again or open in Incognito Mode or private window of browser.
If you try to perform this Example given on MS docs
https://docs.microsoft.com/en-us/dynamics365/customer-engagement/admin/field-level-security#example-for-restricting-the-mobile-phone-field-for-the-contact-entity
You can see this issue coming.
Try to clear your cache and try again.
Friyank Parikh Blog 