Olhando para a documentação da Cisco no NetFlow v9, ela menciona que os bytes O contador é por padrão 32 bits, mas é configurável e sugere que ele seja aumentado para 64 bits nos roteadores principais, etc.
In some cases the size of a field type is fixed by definition, for example PROTOCOL, or IPV4_SRC_ADDR. However in other cases they are defined as a variant type. This improves the memory efficiency in the collector and reduces the network bandwidth requirement between the Exporter and the Collector. As an example, in the case IN_BYTES, on an access router it might be sufficient to use a 32 bit counter (N = 4), on a core router a 64 bit counter (N = 8) would be required. All counters and counter-like objects are unsigned integers of size N * 8 bits.
Assim, o próprio protocolo pode suportar contadores de 64 bits. Parece que o modelo v9 do mikrotik usa contadores de 32 bits.
Acabei de confirmar isso ao capturar o modelo de dados no wireshark.
FlowSet 1 [id=0] (Data Template): 256,257
FlowSet Id: Data Template (V9) (0)
FlowSet Length: 184
Template (Id = 256, Count = 22)
Template Id: 256
Field Count: 22
Field (1/22): LAST_SWITCHED
Field (2/22): FIRST_SWITCHED
Field (3/22): PKTS
Field (4/22): BYTES
Type: BYTES (1)
Length: 4
Field (5/22): INPUT_SNMP
Field (6/22): OUTPUT_SNMP
Field (7/22): IP_SRC_ADDR
Field (8/22): IP_DST_ADDR
Field (9/22): PROTOCOL
Field (10/22): IP_TOS
Field (11/22): L4_SRC_PORT
Field (12/22): L4_DST_PORT
Field (13/22): IP_NEXT_HOP
Field (14/22): DST_MASK
Field (15/22): SRC_MASK
Field (16/22): TCP_FLAGS
Field (17/22): DESTINATION_MAC
Field (18/22): SOURCE_MAC
Field (19/22): postNATSourceIPv4Address
Field (20/22): postNATDestinationIPv4Address
Field (21/22): postNAPTSourceTransportPort
Field (22/22): postNAPTDestinationTransportPort
Template (Id = 257, Count = 21)
Template Id: 257
Field Count: 21
Field (1/21): IP_PROTOCOL_VERSION
Field (2/21): IPV6_SRC_ADDR
Field (3/21): IPV6_SRC_MASK
Field (4/21): INPUT_SNMP
Field (5/21): IPV6_DST_ADDR
Field (6/21): IPV6_DST_MASK
Field (7/21): OUTPUT_SNMP
Field (8/21): IPV6_NEXT_HOP
Field (9/21): PROTOCOL
Field (10/21): TCP_FLAGS
Field (11/21): IP_TOS
Field (12/21): L4_SRC_PORT
Field (13/21): L4_DST_PORT
Field (14/21): FLOW_LABEL
Field (15/21): IPV6_OPTION_HEADERS
Field (16/21): LAST_SWITCHED
Field (17/21): FIRST_SWITCHED
Field (18/21): BYTES
Type: BYTES (1)
Length: 4
Field (19/21): PKTS
Field (20/21): DESTINATION_MAC
Field (21/21): SOURCE_MAC
O campo de bytes tem lenth 4.
Então eu acho que isso deve ser corrigido pelo MikroTik.
A menos que alguém esteja ciente de uma solução / solução alternativa.