Happened totally randomly at round 0.

I just came across this error myself for the first time. Firefox returns "Uncaught TypeError: n is null"

This is the chrome output, which seems cleaner than the firefox output. Firefox has 2 versions, one being rare with less handlers showing, which makes me think it could be the difference of theoretically winning vs. losing. I have not seen anything change in the chrome version. It seems like the "checkForNewRound" function gets called with null as n somewhere. This is the line that's uncaught:
if (n.RoundNumber > t)
The call not providing 2 parameters seems to be this, although I am really surprised why it would work like this anyway and only break sometimes (not having worked with JS):
$(document).on("click", ".seasonalArenaStartNextRound", function() {
var n = $(this);
n.hasClass("loading") || (LW.Buttons.loadify(n),
checkForNewRound(!0))
});
The round completion puts it like this:
checkForNewRound(!0, !0)

lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1 Uncaught TypeError: Cannot read properties of null (reading 'RoundNumber')
at Object.success (lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1:61327)
at l (external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15:39555)
at Object.fireWith [as resolveWith] (external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15:40305)
at b (external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15:75612)
at XMLHttpRequest.<anonymous> (external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15:80474)
success @ lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1
l @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
fireWith @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
b @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
(anonymous) @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
load (async)
send @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
ajax @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
checkForNewRound @ lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1
setTimeout (async)
success @ lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1
l @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
fireWith @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
b @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
(anonymous) @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
load (async)
send @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
ajax @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
checkForNewRound @ lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1
(anonymous) @ lorwolf-bundle.min.js?v=8iETC-dCL-SZJFWhpdSPtkYvFDrQHvoltkEG5WtevnA:1
dispatch @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15
a.handle @ external-bundle.min.js?v=PVMvisFc5k99pdXftUk-yzdgLLhuA1In_VpPwUteaUg:15

Edit: Forgot to add, my battle "team" is a Furmus, with 2 Kapros and 1 Mullvad in the shop, Round 0

Edit2: The output for a successful round, after leaving the game and starting a new one, is entirely different. The combat bundle wasn't even showing up in the other attempt. Now comparing the reloaded chrome tab with my old opened Firefox tab, there is a file called "Seasonal" with the code in chrome that returns this in firefox:
"Error: Incorrect contents fetched, please reload." It is also a folder named "Seasonal" with a file named "Play" instead of a file named "Seasonal" as it is in the refreshed chrome tab.

Edit3: Refreshing the firefox tab fills "Play" with the same content as the "Seasonal" in chrome.

Just wanted to pop in and say that as of 1/16 and 1/17 The frostrun arena has stopped working for me on desktop chrome.

@Stickers @CatCasino @Gilneas

Hi there. I will just ask a few things to help the Dev Team narrow down any potential causes.

- Please take a screenshot of your Team, round, health and the Icerun Arena shop.

- Afterwards, can you manually leave the Icerun Arena game you are in by clicking on the Leave Game button in the top right and tell me if that fixes Arena for you, please? Thank you!

@Darwin Thank you for the bug report. This has been seen by the Dev Team.

@Quiche

@Quiche

Manually leaving seems to have done the trick ! I had tried that before and it hadn't worked, so I guess whatever tiny internal serve error there was worked itself out

@Quiche

it happened again round 1, leaving seemed to kick it back into working order again, but it's been happening off and on but only on round 1 lately

Happening to me, Win10, Chrome Version 120.0.6099.225 (Official Build) (64-bit).

When I try to start the round, I get the little loading dots. Upon refreshing, the round did not play, I did not gain any XP or lose any health, do not have a free refresh.

However: the 'win icerun arena rounds' activity /does/ add one to the count.

ETA: Leaving the game and coming back did fix it. This bug occured on the first round.