I don't know why but in my survival world my arachnid just forgets how to climb for long periods of time

I don't have any other mods except the addons

It happens too in my Aternos server and singleplayer world.

any knowledge of how to fix

The climbing is toggleable, meaning you can turn it on and off by pressing G. It might be that you pressed G accidentally and this turned it off without you knowing, then you can just press G to turn it on again.

thank you comrade