No Sysex output from RNBO VST

I created a step sequencer in RNBO using an Akai Fire midi controller as input device. The RNBO patch sends out the sequenced notes along with some sysex to control the LEDs of the midi controller. When I send the sysex out of max just from the bare RNBO patch, everything works great. But when I export it as a VST and load it in Reaper I can't get any sysex from the plugin.

Here are some things I found out so far:

• some of the midi controllers LEDs are controlled just buy normal CCs and that works just fine. So I think my routing is correct.

• I can send the sysex from the patch in max via a virtual midi cable to Reaper and from there to the controller and everything works fine. So seems Reaper can handle sysex in- and output just fine. (when I do that I can also plugin a midi monitor (ReaControlMIDI) and log all midi signals and it looks as expected: Sysex messages start with F0 and the some bytes and end with F7.)

• For comparison I also exported the "LFO sysex Randomizer-plugin" from Tom Halls machinedrum controlling example (this one) as a VST, but it behaves the same.

I then dug some deeper and read in the Juice forum that sending sysex from a VST3 is broken. (in this threat and this threat). They are saying that the “begin SysEx” byte (xF0) and the “end SysEx” byte (xF7) are not sent out. It is also said (as far as I understand) that sending those bytes twice might help. So I played around with that option and made a little tester patch to send sysex messages in different ways and also sending bytes one by one manually (attached patch).

The only thing I can get from the plugin this way is a sysex message that consists only of the F0 byte. Which led me to this threat reporting that sysex strings from RNBO patches on a raspberry pi can't be longer than three bytes. Not sure if it's the same issue, but looks a bit similar.

Also seems that when using the [sysexout] object even that single byte message isn't sent (in the Plugin, from the Max patch again it works).

I'm a bit at my wit's end. hope somebody can give me the right hint to solve this. Thanks!