According to the SCP document (draft-mazieres-dinrg-scp-04, https://datatracker.ietf.org/doc/draft-mazieres-dinrg-scp/), the following paragraph describes how a node get its higher-layer software's input:
Nodes must not send an "SCPNominate" message until at least one of the "voted" or "accepted" fields is non-empty. When these fields are both empty, a node that has the highest priority among its neighbors in the current round (and hence should be echoing its own votes) adds the higher-layer software’s input value to its "voted" field. Nodes that do not have the highest priority wait to hear "SCPNominate" messages from the nodes whose nominations they are echoing.
However, I think it can be the case that the higher-layer software's input is empty for a node. This leads a questionable case: when the highest priority node has no higher-layer software's input while another node whose priority is not the highest has higher-layer software's input, should this node wait for the highest priority node even though it has its own higher-layer software's input?
Of course, it is not a big problem because the priority of the nodes changes as the round increases, but it seems to hinder the quick agreement.