In net-next there's the following patch which mentions in the
description that it "eliminates spurious list pointer poisoning":
992cba7e276d ("net: Add and use skb_list_del_init().")
And spurious list pointer poisoning is what we see here (IMO).
As an idea this patch and a8305bff6852 ("net: Add and use
from net-next could be applied on top of 4.19. Would be curious
whether it fixes the issue.