If I’m not wrong, this is caused because there are buffer overflows.
In Linux, there are 2 ways (as in API) to access MIDI ports. One is sequencer oriented with lower latency and smaller buffers and the other allows raw access with larger buffers, which is the preferred way for SysEx and the like.
It happens with many applications and libraries that they chose the sequencer API but end up facing this buffer limitation when working with long SysEx messages. Luckily, there’s a workaround consisting in increasing the sequencer buffer size.
This can be accomplished at any time with this.
root@host:/# echo "65536" > /sys/module/snd_seq_midi/parameters/output_buffer_size
root@host:/# echo "65536" > /sys/module/snd_seq_midi/parameters/input_buffer_size
Or can be configured at the module load time like this so you can forget about these issues.
$ cat /etc/modprobe.d/custom-midi.conf
options snd-seq-midi output_buffer_size=65536 input_buffer_size=65536