Fallback handler could not load library E:/Valheim/valheim new/valheim_server_Data/Mono/data-00000268AB5D9010.dll
Fallback handler could not load library E:/Valheim/valheim new/valheim_server_Data/Mono/data-00000268AB5F0020.dll
MissingMethodException: void uMod.IPromise`1.Done(System.Action`1<!0>,System.Action`1<System.Exception>)
  at uMod.Plugins.PluginProvider.LoadOnce (System.Collections.Generic.IEnumerable`1[T] loaders) [0x00018] in <bd89fc329eee4cedbc742caa61c22750>:0
  at uMod.Module.InitializeUniversalAndPlugins (uMod.Common.IInitializationInfo info) [0x00022] in <bd89fc329eee4cedbc742caa61c22750>:0
  at uMod.Module.Load (uMod.Common.IInitializationInfo info) [0x00091] in <bd89fc329eee4cedbc742caa61c22750>:0
  at uMod.Interface.Initialize () [0x0001b] in <bd89fc329eee4cedbc742caa61c22750>:0
  at ZNet.Awake () [0x000f4] in <327b4a0a15454dd5a266954181e42230>:0

I like the little >:O at the end of the lines.

I tried "umod u" and "umod u -APf" but to no avail, error sticks. Server was running fine at 2pm, last restart/update(?) at midnight. Using an old mapsave doesn't help. HDDs have enough space. Second server runs like a charm but has no restart feature (I don't dare to :D).

Should be fixed now, thanks for the report!