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

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.”

Is there any evidence to support the existence of people who have experienced "gangstalking"? Or is it a psychological phenomenon?

Off the top of my ancient head:

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.

What are some reasons why men may not want to date a woman who can pay her own bills?

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.

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

How are Hinduism and Sikhism related, considering they both originated in Punjab, India?

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

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.

Why has no country adopted the SA80/L85 rifle?

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.