I regularly gig (or at least I did before the lockdown) with my BB and RC-300, and I love them both! However, I do NOT have the BB feeding into my RC-300. I feed them into separate channels on a mixer for larger rooms/shows or to separate channels on my Fishman Loudbox Performer amp for small rooms or at home. Vocals into 1 input on the amp. Guitar into bass pedal into RC-300 Into 2nd input on the amp. And BB into aux input on the back of the amp. I don’t know how you have yours hooked up, but would this setup maybe help you?
You can still connect them via midi, although, I have not had much luck with that until I purchased the Onsong app for my iPad, and have slowly been adding the midi programming for 3 devices (soon to be 4) into each song: Voicelive 3 Extreme (VL3X), BB, RC-300. Now, when I navigate to a song, it immediately puts all 3 devices on the correct patches! (When I’m over the PTSD of trying to figure out all the midi programming for all those, I will start to work on how to program the patches for my new keyboard.) :-P.
If any of the above interests you, I can try to find the posts/references for you.
Also, if you’re looking for tutorials on the RC-300, look up “Clayhorse RC-300” on YouTube. His tutorials are some of the best and got me up and running fairly quickly. The RC-300 manual is actually really good, too!—except when it comes to the midi stuff, LOL!