I can tell you what caused the issue for me to miss level 1 rewards, though I know I don't speak for everyone here, of course: I finished my 3 daily objectives in a single game of Squad Battles after the new season had started, so, I had about 900 XP (at level 0), and when I went to turn in my daily objectives, which are worth 500 XP each, I just hit triangle [PS5] as I always do to claim all rewards from that category at the same time. This caused me to go from Level 0, directly to Level 2, from the 1500 XP that it granted me (on top of my existing ~900 XP from the game of Squad Battles I had played already).
So, my immediate thoughts are that because I turned in all of my daily objectives at the same time by hitting triangle [again, PS5, so "Y" on XBox if I were playing on there], that it gave me enough XP for rank 2, and since I didn't individually turn in each daily objective, one at a time, it did not register that I had surpassed level 1... just that now I was level 2 [xp rank]. This most likely caused it to think I already had been rewarded for level 1 on the season, but obviously, I had not.
Hope that helps, and that it's easy enough to understand what I meant, and how it could potentially be replicated in testing to see if that may indeed be part of, if not entirely, the issue.
-Ben H. (Silent-Sniper19 @ PSN)
EDIT: Also, it should be noted, that every season prior, this has never been an issue, so I'd highly suspect it's this, "XP Glitch fix" for season 7 that is the underlying cause of it. It more than likely just refused to reward any players that seemed to have "Skipped" any tiers [XP levels] on the first day, even if just by level 1/one level. So there's another avenue to investigate, if it's not what I have initially posted prior to this edit, as the, Ahem, "XP Glitch fix", has only just now been brought to my attention.
Again, I sincerely do hope that this helps speed things along with your investigation. I'm not trying to be nosey or rude here, I'm just basing this on my own personal experience, as well as my knowledge of how coding and programming works (which is admittedly somewhat limited, but I do have a good understanding of how they work and can affect games or other applications). I'm also not seeking some kind of praises, either. This is just really annoying, not only for myself I'm sure, but for anyone that this may be, or has been, affected by it, and again, I'm merely offering my thoughts for no other reason than wanting to get my level 1 reward faster (the XP player choice pack), lol.
Best of luck, and again, I do hope that this may help. Perhaps just removing the, "XP glitch fix" (especially since it's now been over 48 hours, I believe, since Season 7 started), would fix the issue as well... if that's possible to do without affecting the game or servers in a negative way.