It seems JSON serialization through GSON ends up rounding Long values. Most of the times it goes unoticed, unfortunately, but in some cases we can end up with errors (especially with ES 7.16) as the rounding will take the value out of the allowed range, e.g. for longs:

-9.223372036854776E18 is less than Long.MIN_VALUE, which is -9223372036854775808.