In the 9.1.0 and before, Honedge, Doublade and Aegislash did spawn in Nether Fortress. After updating on 9.1.2, they stopped spawning on the Nether Brick or even any brick. The Wiki do say that they spawn on "Hellish Manmade" and I didn't see anything in the changelog about changing that. When I check with the command checkspawn, no mention of the Honedge's family spawning in the area anymore.

Hi there,

I haven't been able to reproduce this - while standing on nether bricks in a nether fortress, the /checkspawns command consistently returns a chance for the Honedge line to spawn there (output of checkspawns here). The hellish manmade condition also still exists in it's spawning file.

Is it possible you're in another mods biomes which haven't been classified as part of the hellish category? Is there any other mods or datapacks which might be altering spawns? We would need further information as to what's going on here to find and solve any issues.

The private server where I play don't have any mod other than Pixelmon and neither I have.
A screenshot of my checkspawns in the Nether fortress and well, they were almost the only spawn in the fortress, so not seeing anything except some random flying pokemon.

That said, when you talked about biome, that give me the idea to check other structure in the Nether, and in a Bastion after a checkspawns, Honeedge, Doublade and Aegislash was on the list. So I searched for a different fortress than the one I was using... And then the Honedge line was on the list too.

And so, after checking, the biome of the Fortress that don't spawn any of the Honedge line is the warped_forest. The bastion in the crimson_forest and the second fortress in the nether_wastes was working fine.

I had a look at the betterspawner config and confirmed that minecraft:warped_forest is listed under the "hellish" category and looks to work correctly. I tested both a naturally spawning fortress in a warped forest, as well as a platform of nether bricks which I spawned using commands (result of checkspawns here).

Is it potentially the avaliable spawning space which removed the aegislash line from spawning? Do they appear in checkspawns if you place down a large platform of nether bricks?

So, I made a large platform and check if that was the problem and the result is here.
Well, that didn't work. What's really surprising is that in 1.9.0 the place was full of Honedge and it's really after the update that it's now empty.

But, after checking all the fortress, I discovered that after Z:190 the Honedge spawn again, so I created a nether brick platform and found that they don't spawn between Z:-160 & Z:190 and X:-160 & X:193. Also found that they can spawn at Y:129, above the bedrock, even if I place nether brick above the zone that I mentionned. I used creative for checking that, so I checked below that and they can spawn above Y:103, so at least bewteen Y:1 & Y:103 they don't spawn. I didn't check bellow Y:1 for void reason.

I don't know how much that can indicate anything. The fortress I use is placed roughly bewteen the corner at X:28Y:106 and X:-99Y:210. And so i discovered that at the far end of the fortress, the Honeedge spawn like nothing is wrong.

Oddly enough, I was able to reproduce something similar when testing at the coordinates provided in your screenshot!

I found the checkspawns command wouldn't give me honedge across a couple of borders around my world, and found for me these lines were x/z=-112 and x/z=144, leaving a perfect 256x256 area in the middle of the nether where they wouldn't show up on checkspawns. I found that the restriction seems to apply to the player and not the pokemon - if the player is outside the central region but within spawn range of it, then honedge can appear within it (for me, at least). Like you, I found that placing nether bricks on the roof of the nether worked just fine regardless of x/z location, and also down to exactly y=103.

I'll make the rest of the team aware of this and ensure this sees further testing to try and work out what's going on here, and I'll update the ticket when I know more. Thanks!