In general checkmk supports older agents but not newer.
Your agents provides an subsection of df ([df_lsblk_start]) which isn’t handled by the check. From your crash report:
"section_content":
[["tmpfs", "tmpfs", "404612", "45340", "359272", "12%", "/run"],
["/dev/vda1", "ext4", "150558956", "76364964", "66523004", "54%", "/"],
["none", "tmpfs", "4", "0", "4", "0%", "/sys/fs/cgroup"],
["none", "tmpfs", "5120", "0", "5120", "0%", "/run/lock"],
["none", "tmpfs", "2023056", "0", "2023056", "0%", "/run/shm"],
["none", "tmpfs", "102400", "0", "102400", "0%", "/run/user"],
["[df_inodes_start]"],
["tmpfs", "tmpfs", "505764", "1288", "504476", "1%", "/run"],
["/dev/vda1", "ext4", "9568256", "440509", "9127747", "5%", "/"],
["none", "tmpfs", "505764", "15", "505749", "1%", "/sys/fs/cgroup"],
["none", "tmpfs", "505764", "12", "505752", "1%", "/run/lock"],
["none", "tmpfs", "505764", "1", "505763", "1%", "/run/shm"],
["none", "tmpfs", "505764", "6", "505758", "1%", "/run/user"],
["[df_inodes_end]"],
--> ["[df_lsblk_start]"],
--> ["[df_lsblk_end]"]]}}
Can you check your agent output again, if it’s present after the block you already provided?