My 2017 Mazda BT-50 has dropped into limp mode numerous times. It has been to the dealer now six times, each time with a different cause logged on the diagnostic check, including accelerator position indicator, DPF not regenerated, DPF vaporiser solenoid failure, brake fault, and a number of unknowns as the fault is not kept in memory when the ignition is turned off. There is a strong correlation between failures occurring only when the ambient temp is above 28 C, cruise control, highway driving at speed limit, Drive not sport mode. Is this starting to look like a dodgy CPU and/or an engine management software issue, or something else?
With so many different causes logged on the diagnostic check you would have to think it’s something like the ECU, but it’s a hard one to diagnose. You really need to have it happen when the mechanic is there to witness it.