Here two examples of id-less posters in a board with ids enabled
>>>/dump/1085
>>>/dump/1086

to be more specific, every post, when looked at in the moderation mode, has an hash of the ip address
the id-less posts lack any hashed ip, they are basically ip-less, so it's impossible to ban them

this isn't the first time i've seen these odd information-lacking posts on boards, they stand out pretty much usually, but i can't find more examples at the moment

is this an expected behaviour for the site? or what could be causing this occurrence?

>>19088
>>19089
Posters using tor and posting through the onion domain will not have ids or IP hashes.

You can disable posting from Tor in the board settings.

As posters noted above those are users posting via Tor or Lokinet. They don't get IDs or IP hashes, they are all count as 1 poster (on the whole site) and they aren't included the number of posters on the board page.
BOs can disallow the use of Tor on their board, that option was included in case of certain attacks. I encourage you not to choose using it, unless it's absolutely necessary.

>>19090
>>19091
>>19092
I see, thanks for the answers