my 950xl had the same situation. mine is single sim, unlocked, no sd-card inserted, running 10586.0. two days ago, I heard there is .36 update. I checked. nothing there. so I installed the insider app and joined the fast ring. checked again, the .36 is there, together with a fast ring insider update. and the story went on like yours. download completed at 100% and it started to installed. and it failed. error message exactly the same as your screenshot. I tried again. same thing happened again. then I switched to slow insider ring. checked, no update found. then I switched back to fast. checked, .36 (and fast ring insider update) there, but this time it just can't download. it still shows 0% download after 10 hours of my sleep time. even worse, it drained the battery such that my phone was not fully charged even after plugged into a USB of a pc for 10 hours. then I decided to stop the undate. I uninstalled the insider app. rebooted the phone. but I still saw the .36 and insider fast ring update there and 0% for a long time. I reinstalled insider and chose to leave the insider program there. rebooted the phone. nothing changed. still seeing the .36 and insider update. during the said period, the phone occasionally told me I am out of storage space which I had more than 20GB of it. the battery was draining and the update process could not be stopped. finally I factory reset the phone.
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