tf_bots don't like my arena map, anything I can do to negate this?

I could be wrong -- but to my knowledge tf_bots won't work on arena maps. Valve hasn't coded their AI to properly work with the game mode. Which is a shame, it seems as though it'd be easy to do.

A list of game modes that don't have coded

SD_
PLR_
ARRENA_
MvM_ (If we're talking about TF_bots only)

To a lesser degree CTF (The AI works; per say; but some classes (The engineer) get confused often.

You could temporarily turn it into a koth map, with respawns set to 99999 and an instant cap win and test it like that.

I think the problem is that there's no solid objective in arena - a bot needs clear directions on where to go. It's for the same reason that they don't work on plr, where the player can choose either to defend their base or push the cart. That said I don't think using a koth gametype would give you any useful information on gameplay unless the player is actually forced to go to the point, which most arena maps avoid.

Sorry about the roundabout answer.

Type "sv_cheats 1" in console
Type "nav_generate" in console
Wait while the game generates AI paths, progress is tracked in the console
Map will reload (navigation has been saved and the previous step doesn't need to be repeated)
Open console and type "tf_bot_add <number>" as above to add bots
Revert "sv_cheats" to 0 afterwards (optional, but if it is not done, then achievements will be disabled)

Make sure you do the TF_Bot_add because that adds AI, and not the puppet bots.

It should work on arena maps as well.

I did all the things of the above when I was working on my arena map ages ago.
It didn't work for me, and even after lots of googling nothing came up.
As suggested before, just turn it into a KOTH or CTF map