When I first started mystery shopping I came upon the ISS platform. In the first month or so I naively cancelled two shops and got a message stating that if I cancelled again I'd be removed from the platform. Needless to say I then went several years and did dozens of shops for ISS companies without any cancellations, but last month I ended up with two "must cancel" emergency situations and cancelled a day or two ahead of the shop. I noticed that the message now just asks for the reason and states that (paraphrased) cancelling after a shop is overdue counts as a flake and can impact a rating. Have they removed the "3 strikes" policy?
I am unable to directly respond to your query, BUT, I can state my own experience.
Four years ago, I completed three assignments on that platform and then decided it was not my cup of tea. Flash forward to last week when, due to the fees involved, I accepted four jobs, each using the iSS site. WOW! They have certainly changed for the better. My pages appeared fast, were trouble free and the secret agent man was nowhere to be found.
I do not cancel shops frivolously without good reason, and it is rare that I cancel. Since the beginning of the ISS platform, I would estimate that I have cancelled 5 or fewer shops. I always contact the scheduler first so that points (for whatever they are worth) are not lost on ISS.