So what's actually broken?..
Well ... flowStartMilliseconds and flowEndMilliseconds fields in the template are not correctly embedded, putting 1970-01-01 00:00:00 (Epoch) in there. So basically useless.
I've tried some netflow tooling and they cannot really work with that IPFIX data like this. It should be embedded correctly.
As per spec :
(field 152) flowStartMilliseconds dateTimeMilliseconds default current The absolute timestamp of the first packet of this Flow.
(field 153) flowEndMilliseconds dateTimeMilliseconds default current The absolute timestamp of the last packet of this Flow.