This is admittedly an extremely minor bug, but it should also take literally 30 seconds for the appropriate person to fix and is clearly unintentional.

Under the set collection interface of the Profile tab, all of your set collection progress for each set is tracked. These sets are ordered most recent to least... with the exception of the original Ixalan set, which despite being the first set available on Arena is not listed last. Rivals of Ixalan, the second set in that block, is listed at the bottom, with Ixalan coming several sets later.

Upon closer inspection the cause of this issue seems obvious: the release year of Ixalan is listed wrong. The day is correct, but the year is listed as "2018", rather than the correct release year of "2017".

Is this stupid? Yes. But barring some backend weirdness this should literally take the exact amount of time changing an "8" to a "7" takes to fix, and there are few easier wins in this world than that.