Thanks for the response, Zouhair! How frustrating that it is that rare and yet I'm stuck with it LOL!

I have an iPhone 11, though I have the latest version of iOS, so version 15.5, also the latest version of the app, so 4.91. I believe I first installed the app sometime around June 2021, so I probably had iOS 14.6 back then.

I always update everything as soon as the updates are available, it's all set on auto updates. I've tried reinstalling the app a good few times after updates to see if it made a difference but to no avail.

I don't know if this helps, but I also always have the native Apple voice control software active. I normally have it asleep, and only use it to write messages due to having problems with my hands and wrists meaning I like to avoid typing, but it is always switched on.

Thanks again for the response, would definitely be great if you could work out what was causing it so that the app would start working properly on my phone!