My period was delayed by quite a bit when I first started IF. Then my period lasted a long time (like 10+ days).
Once I got that period, though, everything became normal again in the months that followed.
I just started in September and I was delayed by about 4 days this past month. My period was normal once it came and interested to see how it’ll be next month.
Wanted to also add that the podcast called The Fasting Method has an episode about menstrual cycles and may help provide some answers.