I too am having this issue. I have tried from both my phone, tablet, computer, and two different xbox ones in an attempt to get a copy of my world last time I got a successful download my realm was like 2gb give or take. I would really like this issue resolved or at least some information regarding this. ..
I called Microsoft regarding this and we trouble shooted for two hours. I was then informed to contact mojang directly. I have put in a personal ticket as well as reported this bug as I was instructed by the employee who assisted me.
I agree with them. . I spent 2 hours on the phone with Microsoft convinced it may be something to do with my end and they didn't even know this was an on going issue. .. I Love minecraft and I get you guys have a lot of your plate. . But we are paying every month for a broken product... there needs to be a remedy to this.
I have attempted to download it on all 3 platforms associated with bedrock 1.2.1360.70
I have found over a dozen tickets on this very issue. The name of my realm is Regency if that is helpful. I have a lot of players on my realm. I can't afford to lose it because I can't even axcess my own work anymore. This has been an issue for me for over 3 months last time I could get a successful download it was 2gb or so. Please don't just leave this an open ticket not telling us your doing anything about it.