Thanks. So it normal?. Will it get worse?

Should I be getting it replaced?

"Should I be getting it replaced?"

If you want but the next one will more than likely do the same thing. Inherent nature of the wood drying out. Possibly try getting KDAT (kiln dried after treatment) it may slow it down but will still happen to some extent.

Thanks. Will the post still be sound or will it break?. Is it susceptible to water damage?. Could I use screws to keep it together?. Thanks again

It may be sustainable to water but it is pressure treated so nothing to worry about.