I’m not sure if this is part of the same problem, but I notice that for a number of addon airports the ILS frequencies are not visible in the APT/freq pages of default GPSs (G1000, GNS530 up to date with AAU1).
In such cases there is no automatic capture for LOC & GS, if approaching via GPS transitions. I can manually switch from GPS to VLOC and then things work fine, so they’re still in there, just not behaving as normal. If I use the stock airports instead of addons, then things work as expected.
I noticed that Asobo’s own EGGP (Liverpool) suffers from this, so I’m wondering if it’s a bug or at least a gotcha which catches out scenery creators. However this applies to default frequencies, not specifically custom, so it may be a separate issue.