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.

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

Off the top of my ancient head:

Is it normal to hate my dog, but feel too guilty to get rid of him?

Serious disappointment when the client cancels a session.

General Introduction to Boundaries from Panahi Counseling:

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

If I get served by someone else's papers, am I legally required to inform the person that they got served, or the court that they served the wrong person?

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.

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

Do you agree with Michael Moore that Donald Trump is "toast" in a political comeback?

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

Obsessing about clients outside of work hours.

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

Who are the IT boys of the 1st, 2nd, 3rd, and 4th generation in K-pop?

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.