Some have experienced data loss of their entire documents folder and other items. Back up your items and do not apply the update until MS can fix this. If you downloaded the update but it did not install you can follow these steps to delay the installation for 35 days. You also want to check off Pause Updates.

https://pureinfotech.com/prevent-windows-10-installing-april-2018-update-1803/

Here are my sources:

https://www.forbes.com/sites/jasonevangelho/2018/10/05/avoid-windows-10-october-update-until-you-do-one-thing/#371745273e79

https://www.reddit.com/r/Windows10/comments/9levfu/microsoft_windows_10_october_2018_update_can/

@thatwingsy do we know if the data loss is a common thing?
@Dispregio I don't know. But this has happened to consumer as well as enterprise customers. It's probably large enough.
@thatwingsy yyyikes. I'm on the newest update but luckily I have places to back stuff up so I should be ok
@Dispregio That's good!
@thatwingsy @Dispregio The fact it hadn't been found until now means it's likely due to specific combinations of software and hardware. As others said...right now it's hard to pinpoint and most people have gotten on fine with the update. It's derp :(
@ceralor @Dispregio ive read that the preview copy had the same issue but wasnt fixed at release. According to the subreddit thread