Hi, @elnino
Got it. What we see here is an expected behavior based on the information included in the documentation - Configure AD/LDAP Synchronization:
Scroll down to Synchronization Interval (minutes) to specify how often Mattermost accounts synchronize attributes with AD/LDAP. The default setting is 60 minutes. The profile picture attribute is only synchronized when the user logs in.
I hope this answers the question that we have here. Let me know if you have any further concerns. Thanks.