This is very common in freedb with samplers because no albumartist is used. As you don't tell us what's in the filename I cannot tell you how to resolve the problem with the filename.
Have a look at the FAQ
/t/8016/1
Without using the filename you can use two actions or combine them as an action group:
First you have to get the files with the same separator in a row. Then mark all of them.
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Save the calue of the artist-tag to the albumartist-tag
Action Type: Format Values
Field: ALBUMARTIST
Format String: %artist% -
Get artist and title from the title-tag
Action Type: Gues Values
Source Format: %title%
Guessing pattern: %artist%/%title%
or %artist% / %title% or %artist% - %title%
The guessing pattern of the second action depends of the kind of separator in the tags and if there is a white space or not. The separator is always the complete string of characters between artist and title.
Test this with a copy of your files. It does not work properly if the chosen separator character is present in the artist-name too.