Why do my questions randomly disappear as if they never existed?

Probably because of glitches or violations.

Three ways.

1. First, check your profile to make sure it was just not moved to another category.

2. It was a violation and removed.

3. It got zero answers in seven days.

Glitches are also possible.

Either, it was reported and taken down. Or, that annoying glitch has returned where questions would disappear, then reappear hours later.

I remember a few years ago that glitch went on for months and months.

Most Likely Due to a Violation of the Yahoo Answers Community Guidelines

Check the Rule Book to see what you may have Done wrong if After Reading you find you did nothing

Wrong then Appeal use the Alternative Appeal Form

If you got a Violation Email Notice dont use the Link from the Message that one is not working Correctly you will get a Error message saying it did not come from your Account

To Appeal go here

https://io.help.yahoo.com/contact/index?page=conta...

Select Contact a Yahoo Specialist then Appeals then Follow the Instructions from there

If they are no longer in your YA Activity (My Questions) list, then they were reported as violations and removed. If you want to post again here and ask "Was this question a violation" and include the exact text, including any updates, URLs, and images that were included, the experienced users here can tell you if it was a violation or not, and why. A lot of times users post things they don't realize are violations.