Reproducing step:
set vpn pptp remote-access authentication local-users username user1 password 'test1' set vpn pptp remote-access authentication local-users username user1 static-ip '10.10.10.20' set vpn pptp remote-access authentication mode 'local' set vpn pptp remote-access client-ip-pool start '10.10.10.5' set vpn pptp remote-access client-ip-pool stop '10.10.10.254' set vpn pptp remote-access gateway-address '10.10.10.1' set vpn pptp remote-access name-server '1.1.1.1' set vpn pptp remote-access name-server '8.8.8.8' set vpn pptp remote-access outside-address '192.168.255.64'
This happens because module ippool is defined above chap-secrets