Salary did not reflect the level of responsibility. I was given new titles without corresponding compensation.
With a couple of exceptions, senior leadership was often dismissive of women in technical roles. Every woman I worked with in engineering leadership eventually left and has since thrived elsewhere. Watching experienced women colleagues be talked over and ignored discouraged me from contributing as much as I wanted. I was sometimes treated more like administrative support than an engineer, which contributed to the culture feeling very male-dominated. I do think they are at least trying to hire more women - hopefully they hire more women engineers and are able to keep them around.
I also noticed some inconsistencies in how leadership communicated with investors and partners, which at times raised questions for me about company stability. Some of these issues may have been due to normal startup challenges.