Format String Renaming issue

I'm finding format string "Convert Tag To Filename" now moves files to the MP3Tag installation drive e.g. my C: Drive. Before the update the below format string would simply rename the files in the existing directory.

Using the format string:
\%albumartist%\%artist% - %album%[' '][' ('$left(%YEAR%,4)')']$num(%track%,2). %artist% - %title%

Has the string formatting changed?

As you use the backslash, the formatting string also would not have renamed a file but actually have created a relative path.
If the new path also happened to be the old path then you wouldn't notice any difference.
If you only want to rename a file in the current directory then do not add any path-parts to the filename.
The correct mask for a filename only rename would be:
$num(%track%,2). %artist% - %title%

I think that what has changed is your workflow. The root for your relative path has changed. If you add a working directory to the link when calling MP3tag that restores the old root, you should be fine.