I think I've noticed it in other areas of character creation but it is particularly noticeable when I'm picking the arcane tradition for my wizard. It says "one of eight schools: Abjuration, Conjuration, Divination, Enchantment, Evocation, Illusion, Necromancy, or Transmutation" but the only option that appears to be able to choose is evocation. Is this a problem or is there something I've got wrong. I've also seen when I try to pick a feat, it only gives me one option when at times it had given me multiple options (sometimes this happens the other way around) and this can even happen when I've made no changes to the character - it just sometimes worked.

Any help or guidance is appreciated!!!

There are only limited options available for free; one subclass per class, one subrace per race that has subraces and one feat, as well as some spells and magic items not being available for free.

To access the rest of these options, you'll need to purchase the relevant book or option from the marketplace

I'm guessing you don't have access to the Player's Handbook, since Evocation is the only Wizard school in the Basic Rules. If you had access to more feats and subclasses in the past, that character was probably in a campaign where the PHB content was being shared with you, OR you were picking a feat at a time when there were feats available through Unearthed Arcana playtesting.

 I'm having the same issue. I definitely have the PHB, and most of the other source books.