Learn Italian: Questi server sembrano lenti per la latenza. - These servers seem slow because of the latency.

This sentence uses the personal construction of sembrare (to seem). The subject is Questi server, so the verb must conjugate to match it in the third-person plural (sembrano). Because it is a personal construction, the adjective lenti must also agree in gender and number (masculine plural) with the subject.

How would I say this using the impersonal construction of sembrare?

You would use the third-person singular sembra followed by che, and then put the dependent clause in the subjunctive mood: Sembra che questi server siano lenti per la latenza. (It seems that these servers are slow because of the latency).

If there are multiple servers, why isn't the word server pluralized with an 's'?

In Italian, foreign loanwords that end in a consonant (like il server, il computer, lo sport) are generally invariable, meaning their spelling doesn't change in the plural. We know there is more than one server here because all the words modifying it or agreeing with it are masculine plural: questi, sembrano, and lenti.

Could I use a causa di instead of per to mean "because of"?