If you use MusicBrainz Picard's ReplayGain 2.0 plugin to calculate and write ReplayGain tracks, uncheck the "Write reference loudness tags" option; GStreamer will always use fallback gain on tracks that have LUFS reference loudness values stored in them.
For more information, read these two bug reports:
For a long time now I've been confused as to why Strawberry refuses to read my ReplayGain tags. Turns out, it's an issue with GStreamer. There probably aren't many other people affected by this, but I'm making this post hoping that it'll help someone else. 