If you take an advancement with a player/mob head as icon and you open the advancements tab, this icon will become like in the picture in the toast notification, but in the advancements page it's fine. This is probably related to MC-36716.
MC-158293
While advancements tab is opened, heads are bugged in the toast notification
Resolved
Duplicate
0
Lorenzo Federici
(Unassigned)
Unconfirmed
Advancements
1.14.4
Retrieved
Thank you for your report!
We're actually already tracking this issue in MC-69302, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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