Yes — date interpretation is one possible cause, but I would not assume that the MM/dd/yyyy display format itself is the problem. In Dynamics 365 Customer Insights – Journeys, the more important factors are the underlying Dataverse data type, time zone, time component, and how the segment/journey evaluates the related record.
Based on the symptoms, I would investigate the relationship/multiple related records first, followed by Date & Time/UTC handling.
If the requirement is simply:
A contact should be included if they have at least one associated item whose date is today or in the future.
then I would explicitly design the segment around existence of a related item meeting that condition, rather than filtering contacts based on whether a related item has a past date.
Also, if the field represents a business date rather than an exact point in time, I strongly recommend changing/using a Dataverse Date Only column. This eliminates many unnecessary time-zone issues in Customer Insights journeys.
