Problems with TTFB

Hello everyone I need help.

When I open the start page, it loads pretty quickly. But when I go further, the page opens very long. When I open it again, the download time decreases.

Help me to understand.

Thank you.

http://www.webpagetest.org/result/170926_1K_908b4e64a39501f3d2138f299fdcb453/
http://www.webpagetest.org/result/170925_B8_59fbd044166a381d1d6c797b069864cb/