This happened at the time when mods were very actively being updated on the workshop, shortly after Airports update was released.
The Mod C:\~~\2399343344 [Mono.Cecil.dll, MonoMod.Common.dll, IAmAware.dll, 0Harmony.dll, 0Harmony.dll, 0Harmony.dll, CitiesHarmony.dll, CitiesHarmony.Harmony.dll, HarmonyMod.dll, Mono.Cecil.Mdb.dll, Mono.Cecil.Pdb.dll, Mono.Cecil.Rocks.dll] has caused an error [ModException]
Details:
System.NullReferenceException: Object reference not set to an instance of an object
at HarmonyMod.Report+<>c__DisplayClass38_0.<OnModListChanged>b__2 (ColossalFramework.Plugins.PluginInfo p) [0x00000] in <filename unknown>:0
at HarmonyLib.CollectionExtensions.Do[PluginInfo] (IEnumerable`1 sequence, System.Action`1 action) [0x00000] in <filename unknown>:0
at HarmonyMod.Report.OnModListChanged (Boolean inGame) [0x00000] in <filename unknown>:0
at HarmonyMod.Mod.ICities.ILoadingExtension.OnCreated (ILoading loading) [0x00000] in <filename unknown>:0
at LoadingWrapper.OnLoadingExtensionsCreated () [0x00000] in <filename unknown>:0
This happened at the time when mods were very actively being updated on the workshop, shortly after Airports update was released.