For anyone fighting with PoC for low-priv shell- the machine is working and the vuln is available. The PoC script is purposefuly left incomplete by the creator. Read the script and add missing parts. Think how HTTP retains state between requests and make sure your state is remembered between them.
DO NOT i repeat: DO NOT restart the machine to ‘fix’ that. It will achieve you nothing but a nervous breakdown of fellow hackers. Read and understand the scripts you’re using, learn to debug them instead of random resetting the machines ya skiddies.