Just in case someone arrives here with this issue, the solution for our case was to add a line to app.config <AppContextSwitchOverrides value="Switch.System.Globalization.NoAsyncCurrentCulture=true"/>
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<?xml version="1.0" encoding="utf-8"?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8"/>
</startup>
<runtime>
<AppContextSwitchOverrides value="Switch.System.Globalization.NoAsyncCurrentCulture=true"/>
</runtime>
</configuration>
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In .NET Core these properties are implemented as `AsyncLocal<T>`'s which in short means that any updates to them only affect the current asynchronous control flow, such as an `async` method.
Depending on what you are trying to accomplish, you may consider to create and set your own static `CultureInfo` properties.
On .NET Framework 4.6 and later, you could set the `NoAsyncCurrentCulture` switch to `true` in your `App.config` to get back the old behaviour:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8"/>
</startup>
<runtime>
<AppContextSwitchOverrides value="Switch.System.Globalization.NoAsyncCurrentCulture=true"/>
</runtime>
</configuration>
[<AppContextSwitchOverrides> element](https://learn.microsoft.com/en-us/dotnet/framework/configure-apps/file-schema/runtime/appcontextswitchoverrides-element?WT.mc_id=WD-MVP-5001077)
[Retargeting Changes for Migration from .NET Framework 4.5 to 4.6](https://learn.microsoft.com/en-us/dotnet/framework/migration-guide/retargeting/4.5-4.6?WT.mc_id=WD-MVP-5001077)
