Some statistics in 2.4 use plain int types for statistics which overflow into negative values. Depending on the statistic it might take longer but the counter for the number of executed queries is the most problematic one.
This is not a problem in 2.5 where the statistics were converted into the generic statistics object.
The JSON library used by MaxScale doesn't support unsigned 64-bit values. To correctly handle statistics that are stored as unsigned 64-bit values, they must be made to fit the positive range of the 64-bit signed integer. This isn't really a problem in practice as most counters in MaxScale grow slowly enough to never wrap around.