iMovie on iPhone export error.

I have tried about 20 times to export a video from iMovie onto my phone, however it keeps coming up with an error warning reading that there has been an error exporting the movie. This comes up when the export has reached 95-99% complete.

I have tried on all qualities, I have restarted the app, switched my phone on and off, cut the video and even tried opening the video with a photo (all suggestions I came across) and nothing. I also have plenty of storage available on my phone.

I exported a video with no problem on Sunday and also last Thursday with no issues, and I have never seen this error before. Unless a new length limit has come in, it's not due to the length of the video, as around a month ago I exported a video which was over 40 minutes long with no hassle!

The only other thing that may affect it is that I'm not connected to wifi whereas I usually am, but I'm pretty sure that doesn't effect this?

Please help as I am a youtuber and I rely on this to get my uploads sorted!

Many thanks :)