I guess that would depend on the partner? And what do you mean by vulnerability in that context that would make her lose respect?

And what do you mean by wrong times or reasons?

Most people seek emotional support, resilience and trustworthiness from their partner, and being excessively "vulnerable" can definitely hinder you from playing that role effectively. This is what can sometimes be experienced as a loss of respect. What you really want is to show a mere modicum of emotional vulnerability that your partner can then have some opportunity to empathize with, and not view you as overly brittle. But not more than that.