Brett, thanks for updating me on this. VS text files have a 'language service' assigned on load based on their extension, which provides syntax highlighting and Intellisense among other things, but which more or less free reign to do what it wants. There are many stock language services installed with base VS (for C, C++, C#, VB, etc...), and other extensions can install extra language services. As far as I know, there can only be one language service loading for a given editor window.
Files with a ".config" extension are probably triggering the load of some specific language service, and that language service is interfering with Esc. Because, what extension/add-in/language-service/random package does not want to do something unique with Backspace, Enter or Esc and is not thinking about the potential impact on other extensions? Pardon my passive aggressive rant, just trying to drive the point across.
You might have some luck if you're not using anything special from the .config language service and you can configure things so that the language service is not loaded. This documentation page shows how language services are configured in VS:
https://docs.microsoft.com/en-us/visual
ew=vs-2019
Apart from a language service, the issue may be caused by a MEF extension (the newer way to intercept and disrupt all kinds of things, which ViEmu of course uses to provide vi/vim bindings after VS2010). When the issue is file-extension-specific, it is usually about the language service, but it may not be the case. If it is a MEF issue, then all bets are off, you may just need to try enabling and disabling every extension in your installation of VS, since the MEF tree build and data/event distribution in MEF is obscure, poorly documented, undebuggable, and prone to all sorts of issues (as you saw yourself).
I will have a look at it at some point though, to see if I can find what the issue may be.
Cheers,
-- Jon