That is a red flag according to me. If you don't have anything fishy why would you be defensive and secretive. Now a days people spend a lot of time in office. Maybe there is something even they cannot wrap their head around.

Early red flags people usually ignore are subtle changes in behavior. It’s not about normal workplace friendships those are completely fine but sudden secrecy, defensiveness over simple questions, or emotional distance. If someone becomes overly protective of their phone or reacts with anger instead of reassurance when asked calmly, that’s when it starts to feel off. The biggest sign isn’t one dramatic incident, it’s a consistent small shift like, minimizing your concerns, or making you feel insecure for even asking.

At the end of the day, it’s not overthinking if there are repeated behaviors that create confusion. Healthy relationships make you feel secure and respected, not doubtful or dismissed.

Trust your gut!