Have reviewed your install. This is due to "Auto-recurring renewals (*):" being set to "Yes: subscribe user to automatic recurring payments (*)". For lifetime plans that needs to be set to "No: single payments at a time". Please adjust all your lifetime plans accordingly.
Note this is working as intended. You can't auto renew lifetime plans. In a case where this plan wasn't free and you tried forcing lifetime recurring it would cause a lot of issues for gateways (it'd just be rejected or capped at the maximum of 1 year for most gateways).
It could probably handle this scenario a little better, but is likely a usecase just not completely considered as it doesn't make any sense. Free lifetime could technically just ignore that parameter entirely and have added a bug ticket regarding this.
#6848