A bad description, but I am completely do not know the forum engine to describe the problem properly and to ask exact questions instead of “how to search in logs” as I did in the support ticket:
And another one off topic but Discourse bug reporting related - how to get forum engine version:
So may be somebody can check our forum logs to know when ‘likes’ undo timeout was introduced: if that was actually configuration change of forum engine, so may be not a bug? The link to such logs is in the answer of the thread linked above: Lost ability to undo own 'like' mark on a post - #2 by Falco - support - Discourse Meta