Cpanel::JSON::XS versions from 4.42 before 4.80 for Perl let input chunking change the decoded value of top-level numbers in incr_parse. allow_nonref is enabled by default and incr_parse inherits it. A top-level number, true, false or null has no closing delimiter, so the incremental parser decodes whatever has arrived. The bytes 12 decode as one value when read together, but as 1 and then 2 when split across two reads. A peer that can influence read boundaries can change how many messages a stream consumer decodes and what values they carry.
https://metacpan.org/release/RURBAN/Cpanel-JSON-XS-4.80/changes
https://github.com/rurban/Cpanel-JSON-XS/commit/f632d6690d82c14cd2d76d648805325201c52b83.patch