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

Obsessing about clients outside of work hours.

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

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

Did Leonardo da Vinci paint two Mona Lisas? Where are they?

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.”

Off the top of my ancient head:

China tightens ‘whole-chain’ control on critical minerals amid US pressures - South China Morning Post

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

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

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

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Serious disappointment when the client cancels a session.

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

General Introduction to Boundaries from Panahi Counseling:

Why is the mainstream media, traditionally liberal except for Fox, not reporting on Trump like he's a traditional candidate who has ideas, values, and a concern for the common good?

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.