It sounds like there are no CAN devices acknowledging your messages. (Some devices are listen-only devices or can be set to listen-only.) If no devices acknowledge your message, the message stays in the write buffer and gets sent repeatedly until a device does acknowledge it. Meanwhile your single frame writes can't be sent and are overflowing the buffer. Here's what you can do:
A) Configure your device to acknowledge messages, or
B) Attach another device to the network to acknowledge messages. (ie You can attach another NI CAN port to the bus and just configure a network interface object with a comparator of CFFFFFFF.)
If this does not work, let me know what happens. By the way, if you never write any of the single frames, do your period
ic messages still stop?