This is an unresolved issue in ASP.NET which was first reported in 2019:

• https://github.com/dotnet/extensions/issues/1171
• https://github.com/dotnet/runtime/issues/35989
• https://github.com/dotnet/runtime/issues/87130

There is a workaround which allows '___' (triple underscore) to be used instead of '.' (link)