List of steps to reproduce (step by step, including full links if applicable):

Order may be very important here:

1. Start a new private browsing session in Firefox
2. Enter responsive design mode (Crtl-Shift-M)
3. Select "iPad" from the drop-down
4. Go to https://en.wikipedia.org/
5. Click the "Desktop" link at the bottom of the page
6. Log in to an account eligible to vote in the current ArbCom election
7. Go to https://en.wikipedia.org/wiki/Special:SecurePoll/vote/801
8. Click "Go to the voting server"

What happens?:

I am taken to https://vote.m.wikimedia.org/wiki/Special:SecurePoll/vote/1303 and see "You must log in to vote in this election - please try following the link from your Special:SecurePoll on your local Wikimedia site."

What should have happened instead?:

I see "Welcome Suffusion of Yellow!"

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:

Mozilla/5.0 (X11; Linux x86_64; rv:94.0) Gecko/20100101 Firefox/94.0 in responsive design mode, simulating "iPad", Mozilla/5.0 (iPad; CPU OS 14_7_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1.2 Mobile/15E148 Safari/604.1)

Others have reported this on "real" mobile devices, see https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&oldid=1056840719#Unable_to_login_to_the_secure_poll_for_the_ACE

Workaround (2022)

Some editors have reported that "changing back to the desktop view on VoteWiki" (i.e. clicking the "desktop" link in the footer on VoteWiki) allows them to then vote successfully — the "desktop" link goes to https://vote.wikimedia.org/w/index.php?title=Special:SecurePoll/vote/1402&mobileaction=toggle_view_desktop, and visiting that URL directly may work for you if you are already logged in.