Sorry for note getting to you earlier, your question is relevant. Did you manage to move forward in the meantime?
Anyway, while I have little direct experience with Bayes factors, they tend to be finicky and hard to get right, so it is possible you are just hitting one of the problematic situations. I also noticed you have increased adapt_delta and changed inits, so I presume the models had problems otherwise? If so, it is likely that computing bayes factors has a bit stricter requirements on the model behaving “nicely” than just fitting with brms and you might need to address the underlying problems before being able to compute Bayes factors.
I’ve also previously written about alternatives to Bayes factors for model selection/comparison: Model comparisons and point hypotheses so this might help as well…