Just trying to work out what you are using.
The original filter was labeled 1090MHz, (light blue) but is in fact the same as the current 1090+978MHz filter (also light blue).
Recently a narrow band 1090MHz filter has become available (dark blue).
The insertion loss is about the same (at 1090MHz), so really shouldn’t make a difference, but if you’ve replaced like-for-like, the problem is definitely elsewhere.
