Bug overview description.
e926 shows e621 in "safe" mode, including SFW ads. (Which I appreciate.) However, when you view the site on mobile, or have the desktop window narrow enough to switch to mobile mode, it instead shows adult ads.

What part(s) of the site page(s) are affected?
At least image pages and the search page. I expect anywhere that shows ads and has a mobile mode would be affected.

What is the expected behavior?
e926 will show only SFW ads, whether in desktop mode or mobile mode.

What actual behavior is given instead?
e926, when in mobile mode, shows NSFW ads.

Time of incident (if applicable).
Uh, 2021/02/18, ~5:00-5:15 EST, but probably not related to time.
I suspect this bug was not always present - I'm pretty sure I've used e926 multiple times before on my phone, and would likely have noticed if it was showing NSFW ads.

Can you reproduce the bug every time?
So far, yes.

What steps did you take to replicate this bug?
Opened e926 on mobile, noticed bug. Opened e926 on mobile in incognito, observed bug. Opened e926 on desktop, no bug, resized window smaller until it switched to "mobile mode", refreshed page, observed bug. Refreshed several times in all conditions. (Also tried changing the desktop user agent to be mobile, but that had no apparent effect on the mode.)

Errors or other messages returned (if any).
None.