I sent a message to Orbit Customer Support and got a very quick reply for the above issue.
They noticed that the addresses on my hose timers were slightly different to my indoor/ outdoor timer. Not sure if this would be causing the problem because the difference was between my actual street address and just my suburb address. I updated these but then noticed that all three of my hose timers were connected to a different weather station to the one my indoor/ outdoor timer was. This is more likely the cause of the problem. I’ve now updated them all to the same weather station.
Hopefully the next time my indoor/ outdoor timer gets a rain delay the three hose timers also get them. Will keep you posted.
I suggest checking you settings to make sure all your timers have the same weather stations. Not idea why the hose timers had something different to the indoor/ outdoor timer.
Also suggest contacting Orbit directly via their support page because I had a reply to my message within 24 hours.
Still waiting for another issue I raise with them where I can only add a rain delay on the hose timers when connected via Bluetooth. If connected via WiFi it does not work.