Why is my 2019 MG GS' check-engine light often on despite being regularly serviced?

You could be looking at a couple of problems here. Either there’s a recurring problem with the car that is causing the check-engine light to illuminate, or the problem was fixed at one of the four previous service appointments, but the service team has consistently failed to zero (reset) the warning light.

In most cases, these check-engine lights are cancelled via the on-board scanning process which, coincidentally, would also tell you if there’s a constant problem forcing the check-engine warning to light up. Either way, it’s back to the workshop for an electronic vehicle scan to rule out the latter and/or reset the former.