Sorry if this was correct behavior.
When I tried to combine enchantments in 1.7 with the same content as in 1.8 with an anvil, the required levels are different.
Then combine them and close inventory, they were canceled and the level disappeared. (The level came back when I made an action that would update the level.)
However, using the same level as 1.8 was worked.
The same thing happens not only with swords but also with armor.
Sorry for bad english.
Prepare the sword using the enchant command and the book using the enchant table.
Place the anvil and work as in the video above.
Expected Behavior
If the required level is enough, it is not canceled and the levels are consumed and combined.
(I think it is unavoidable that different versions have different levels of requirements.)
Additional Server Info
I deleted all the files and downloaded PaperSpigot 1.8 again.
The only plugins installed are ViaVersion and ViaRewind, ViaRewind-Legacy-Support.
And I do not use proxies.
Checklist
[X] Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. BungeeCord), not on both.
[X] I have included a ViaVersion dump.
[X] If applicable, I have included a paste (not a screenshot) of the error.
Barvalg
commented
4 months ago 
-Even%20with%20master-brightgreen?style=flat-square){kind=icon}
-Even%20with%20master-brightgreen?style=flat-square){kind=icon}
/viaversion dumpOutputhttps://dump.viaversion.com/0713a343db61d8ba175f4358d6e5b3ccd1d4fc1aa73837cf433f674bed592389
Console Error
No Errors
Bug Description
Sorry if this was correct behavior. When I tried to combine enchantments in 1.7 with the same content as in 1.8 with an anvil, the required levels are different. Then combine them and close inventory, they were canceled and the level disappeared. (The level came back when I made an action that would update the level.) However, using the same level as 1.8 was worked. The same thing happens not only with swords but also with armor. Sorry for bad english.
1.8 Video (Worked) https://github.com/ViaVersion/ViaRewind/assets/80197107/664c0c36-cc33-449a-9e54-70b1b53db589
1.7 Video https://github.com/ViaVersion/ViaRewind/assets/80197107/2f4890ea-a6db-4b6d-b9c6-507571aa39f2
Try combining at 1.7 with the same level as 1.8. (Worked) https://github.com/ViaVersion/ViaRewind/assets/80197107/e71abb85-d56d-4743-9174-324f94bac653
Steps to Reproduce
Expected Behavior
If the required level is enough, it is not canceled and the levels are consumed and combined. (I think it is unavoidable that different versions have different levels of requirements.)
Additional Server Info
I deleted all the files and downloaded PaperSpigot 1.8 again. The only plugins installed are ViaVersion and ViaRewind, ViaRewind-Legacy-Support. And I do not use proxies.
Checklist