That happened when I lived in NM and went running. I had to wear a lot of sunscreen and I was sweaty, and it's the desert. My legs were always crusted when I was done.
I generally wear pants or a long skirt and try to avoid shoes any time I can. So no not a problem for me. Rub it in more? wait for it to absorb? I don't know.
Not just flip flops....any shoe with shorter pants depending on if it's wet outside, otherwise not as much. I could see lotion picking things up if your skin hasn't fully dried