UPDATE: This issue is very complicated. I tried all tips in previous comments. This is my current tests and diagnosis. If this can be shared with apple someone please call this info in. I have HDR turned off, most compatible selected and have tried these sent to my wife's Galaxy S8+ on Verizon:
1) 21 seconds, 38 MB, at 1080p 30 fps sent successfully but real bad quality on wife's phone
2) 22 seconds 19 MB and 40 seconds 33 MB at 720P sent successfully. Quality is better than the 1080p but still a little blurry.
3) 1 min 1 sec 55MB at 720p not sent successfully. Tried to downsize the quality with an app and sent it at 1 min 1 sec and 19mb and it still didn't send.
Conclusion is very confusing. It can send at 1080p for 21 seconds at 38mb. Can send at 720p for 40 seconds at 33mb. But cannot send 720p past 1 minute of video even though it was shrank from 55mb to 19mb.