After upgrading Resharper to 2021.1.4, ForTea gets namespaces confused

Having updated Resharper to 2021.1.4, using VS Enterprise 2019, now ForTea seems to assume that my tt template must be living in a different namespace than it really does. It appears to be marking my partial class as not related to the T4-generated code, thus signifying that private variables and methods that I have for the T4 template can't be found.

Note that when I build, the solution builds fine, this is largely a visual issue, which also affects Intellisense so completion of variables and methods no longer work.

For example, in my partial, I say that this is an `ITemplate`, which has `public string TransformText();` in the interface. That is, of course, implemented by the T4 generated code, but Intellisense + ForTea thinks that this isn't met, so I get the red squiggles. Further, my partial has a function `public string Html(object o) {...}` and a field `private readonly string _foo;` and inside the tt file, where I have `<#=Html(_foo)#>`, both `Html` and `_foo` are in red as not-found, even though the compiler is perfectly happy.

This seems like a bug in either Resharper and/or ForTea.