Recently started a new realm on Minecraft Bedrock. Myself and another player have each had a librarian reset their trades after the librarians had been previously traded with (my mending for 22 emeralds librarian changed to Infinity for 14). In both cases the librarian maintained the same exp level.
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This isn't the same as the cited duplicate. For my example I had a librarian with a mending book for 22 emeralds locked in (I had traded with the librarian) I moved this villager's lectern inside a house and went to trade with the same villager and found that his experience level remained the same but his trade switched from the mending book for 22 emeralds to a Infinity book for 14 emeralds. This has never happened before to me.
My wife had a similar issue with a villager who had a luck of the sea 3 book locked in and when she went back to trade with this villager again the trade switched from luck of the sea 3 book to a bookshelf. This all happened within the same few hours on our server.

Based on comments and other issues linked to MCPE-117852, that does seem to be the same issue, which is that the items for trade change, even though the profession doesn't in your cases. It likely happens when the villager re-links to the workstation.

Umija5859M I can see that similarity now that you put it that way. In my situation there were not any other available job blocks.
Hopefully a solution to this issue is found and resolved soon.
Thank you.
Thank you for your report!
We're tracking this issue in MCPE-117852, so this ticket is being resolved and linked as a duplicate.
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