Issue with iCloud Calendar on browser

I've been using iCloud calendar for a long time in my phone and also in computer without any complications. Today when I opened the calendar on browser all the "all day" events were spread out on two days, although they're set on one day. Also I've set my time format on 24h, but now it shows everything in 12h format. I've already tried changing it. I've also checked my time zones on both devices and everything is correct. Everything seems to be fine on my phone calendar.

I installed a new iOS on my phone, could the issue be in that somehow?

[Re-Titled by Moderator]