interop.illustrator .net c# Failing on 27.01

We have a longstanding application written in C# .net that calls and instructs illustrator using the COM interop.illustrator. This has worked fine for many years up to 26.5.1.

On upgrading to 27.01 the application suffers frequent errors when running as if the interop has lost contact with Illustrator. It's always been a little touchy, but, adding thread pauses always seems to work. However, the code runs fine on 26.5.1 but fails frequently on 27.

Has anyone else had the problem? We're using the latest version of Visual Studio Professional and .net framework.

Thanks.

B