Brms

[andre.pfeuffer]

The message is not good. You should be concerned.
It occurs when a log is near 0, so it falls out of precision and log(0) gets evaluated.
This thread should give you hints about how to solve this issue:

Rejecting initial value using non-logit link for cumulative ordinal models

I think the default priors are flat in brms, so that could be an issue too. Manually specifying at least a weakly informative prior is usually a good idea.