This article explains possible reason for flowd crash on SRX / VSRX platforms.
After changing syslog format to "protobuf", device cores and recovers normally after the crash. It happens due to memory corruption in the code handling protobuf logs.
Since it is memory corruption trigger may or may not happen immediately, It make take minutes to months for hitting this scenario.
Issue is fixed in : junos:25.4R1 junos:25.4R2 junos:26.1R1 and latest versions.