R Ashwin hadn't bowled a front-foot no-ball in close to 3340 overs across 74 Test matches before the Chennai Test against England. In his 75th Test, however, he was called for overstepping five times in his 73 overs. Shahbaz Nadeem and Jack Leach were called for overstepping in Chennai too, while in Karachi, Yasir Shah and Nauman Ali bowled no-balls against South Africa. There were quite a few errant spinners in the Chattogram Test too - Jomel Warrican alone sent down five. This isn't a surprise, really. It's the result of TV umpires taking over on the adjudicating on no-balls.
Spotting no-balls is not as easy a task for the on-field umpire as it may seem, as noted here. On-field umpires were calling no-balls only when they were absolutely certain of the infringement, which carried an unwritten benefit-of-doubt clause within it. But since the ICC put front-foot no-balls on the TV umpires' plate in July 2020, there's been a spike in the number in Test cricket, and that benefit of doubt has vanished.
While a rise in the number for fast bowlers overstepping was to be expected, it has come as a surprise that spinners have erred as often as they have. After all, theoretically, the on-field umpires have more time to look at the popping crease and up at the batsmen when spinners are bowling compared to when quicks are in operation. They should, therefore, have missed fewer no-balls from spinners than from pacers. And so, the increase in no-ball calls against spinners should have been lower when compared with fast bowlers. However, the numbers tell a different story.
Since the Pakistan tour of England in August 2020, spinners have sent down 63 no-balls in Test cricket - one every 216 deliveries (or 36 overs). Compare this to the period between August 2018 and July 2020, when spinners were called for overstepping only once in every 263 overs. That is, they've been called for no-balls seven times more frequently after TV umpires took over.
Meanwhile, fast bowlers are being called for overstepping once every 117 deliveries since August 2020, down from every 275 deliveries in the two-year period before that.
One possible reason could be that years of conditioned thinking - that spinners don't bowl as many no-balls as fast bowlers do - had lulled on-field umpires into being less watchful when spinners operate. This could have had a knock-on effect on spinners too. You haven't been pulled up for bowling a no-ball in ages and, therefore, it isn't a problem you need to pay attention to at the nets.
Some more numbers to chew on: Since August 2020, 40 spinners have bowled in Test cricket, and as many as 20 of them have bowled at least one no-ball; in the two years before that, 82 spinners bowled, but only 21 were called for overstepping. The number of spinners being no-balled has nearly doubled. More and more fast bowlers are being spotted overstepping too, but the spike - from 53.2% to 68.6% - is not as alarming.
The graphic above lists the top ten spinners in terms of balls bowled from August 2018 to July 2020 and the number of no-balls they sent down in that period. With the exception of Nathan Lyon and Roston Chase (the latter has bowled only 38 overs since), all bowlers have bowled at least two no-balls since August 2020. Each of them had bowled around 300 overs in Tests before this period and, with the exception of Ravindra Jadeja, been called for no-balls only once at most. This suggests, again, that spinners were overstepping often, just that it wasn't being spotted.
A look at Shannon Gabriel's no-ball stats tells us that on-field umpires might be paying more attention to repeat offenders - and spinners have not been among them traditionally. Gabriel's frequency of bowling no-balls has actually improved, indicating that he's not been adversely affected by the change in TV umpires calling no-balls. In 325 overs between August 2018 and July 2020, Gabriel was called for overstepping 31 times - once every 63 deliveries on average. Among 20 fast bowlers to have bowled at least 300 overs in that period, Gabriel was the worst offender, by a distance at that. Ben Stokes - the next worst - sent down 44 more deliveries on average before he overstepped. And since August 2020, there have been nine fast bowlers - among those who have bowled at least 25 overs - who have transgressed more often than Gabriel has.