dfk41 That looks yum mate. 😋
I do not bake as regularly as I would like. IMO, the method and ingredients look solid for a classic honey cake. I think issue is it’s a very wet, heavy batter (lots of honey and melted sugar, no creaming for air) baked quite gently, so it rises fine but the structure sets late and then drops back a bit as it cools.
To see if that fixes it, I would reduce honey may be by 25-35g, increase flour by an equal amount, add ½ tsp of baking powder, and bake a little hotter (160 fan / 170 conventional for 50-60 mins (not checking before 40-45 mins). These changes may give a bit more support to stop the cake from sinking. I assume you are lining the tin (at least the base). It will taste as fine as before as you still have got a lot of honey and sugar.
Edit:
Deeper the tin, the slower the cake sets especially at the centre coupled with trapped steam. They require additional heat.
You may also add a pinch of salt as it may help tighten the crumps.