Hello John,
Sometimes, when a
segment field like
ConversionTrackerId is used, it results in significantly increasing numbers of rows for a result, thereby affecting the overall performance of reporting system.
That's why in some cases, a certain field is prohibited to be used with such a segment field.
To confirm if this is the case for Conversions and ConversionTrackerId as well, I need to consult with engineering team first.
I will get back to you later when I get updates.
Cheers,
Thanet, AdWords API Team