What are some signs that a therapist may have poor boundaries with their clients?

Eager anticipation (or anxious anticipation) of the next session in ways that distract.

General Introduction to Boundaries from Panahi Counseling:

Sense of competition with persons who are important in the client’s life.

Is sunscreen toxic? The UV truthers on the internet sure think so. - The Boston Globe

Failing to mention the client in supervision/consultation, out of fear the supervisor/consultant will advise return to ordinary healthy boundaries.

Struggling with fantasies of deeper connections with clients, whether sexual or parental or other intense or intimate relationships beyond psychotherapy.

Disclosing feelings, fantasies, and experiences to the client in ways not related to the work the client is engaged in.

The Roman Empire at the time of Christ kept meticulous records. Why then, is there no record of the trial of Jesus?

Session-expressed curiosities about client details not relevant to the therapy.

Frequent phoning or texting of clients to “check up on them and make sure they’re OK.”

Obsessing about clients outside of work hours.

How Moderna Went From Pandemic Hero to Vaccine Victim - WSJ

Off the top of my ancient head:

Serious disappointment when the client cancels a session.

Routinely going over the time limit with certain patients, compromising the time for the next client.

Satellite Scanning the World’s Oceans Detects Elusive Phenomena Scientists Say Had "Been Hiding in Plain Sight - The Debrief

These items can happen fleetingly, briefly, in any therapy, but if they’re frequent, it’s definitely time for the therapist to get some good, solid supervision/consultation.