Update: I was inattentive to the fact that ἀξιόθεος is a two-termination adjective, and therefore masculine and feminine forms are morphologically fused. Thanks to Jack for pointing this out in the comments.
I just started reading Ignatius' letter to the Trallians and came across an oddity. In the opening sentence, Ignatius notes that the church to which he is writing ἐκκλησίᾳ) is "worthy of God" (ἀξιοθέω). Since this adjective is modifying a feminine noun, I would expect the feminine form here. It happens to stick out like a sore thumb because Ignatius is using many adjectives to describe the church and they are all in feminine form (ἠγαπημένῃ, ἁγἰᾳ, κτλ), save this one.
At first I remarked to my wife: "there's a grammatical mistake in this sentence." But after considering it for a minute, it seems most likely that Ignatius put this adjective in the masculine form due to θεός being statically male in the Christian tradition. It probably "sounded wrong" to use the expected feminine ending.
I checked BDAG and found that there are attestations of ἀξιόθεος being declined for a ~~feminine~~ noun (Update: actually neuter in this case), including in Ignatius' letter to the Romans, 1:1. I am not sure if this is due to Ignatius' own idiosyncrasies, or due to transmission or spelling normalization by an editor. At the very least it was not a hard-and-fast rule, since we see both forms by the same author.
Additionally in the salutation to Romans, Ignatius does this same switching back and forth between feminine and masculine forms in describing the church. Perhaps someone has already done some research on this phenomenon, or perhaps there is a paper waiting to be written on this topic.