As told to Valentine Low (the journalists the former employees first approached) and recounted in his book Courtiers, one former staff member gave a detailed account of Meghan’s behaviour towards them on one Friday night in particular. Something had not been to the Duchess’ satisfaction and she and Harry continuously rang their staff member to berate them.
"Every 10 minutes, I had to go outside to be screamed at by her and Harry. It was, 'I can't believe you've done this. You've let me down. What were you thinking?' It went on for a couple of hours. You could not escape them. There were no lines or boundaries—it was last thing at night, first thing in the morning,"
This is malicious bullying, absolutely. And that’s just one of the stories. He recounted plenty more. (I’ve investigated these kind of complaints before, too. They are easy to verify, or refute - ask to see the employee’s phone records for the night in question. If it’s a work phone, get the employer to get the phone records. So, easily verifiable, and set out in detail in a published book…).
Plus the fact that a official complaint was made to HR about Meghan’s bullying staff at the time, and Harry admits in his own words in Spare that their office was a toxic environment and his brother (who also worked with the staff) was concerned about Meghan’s behaviour. This is not some spurious gossip, there is plenty of evidence making it look more likely than not, unless you are determined to close your eyes to it.