The conjunctions are possible if, in each of the RVCs, the resultative complement is removed:
Fàn zuò le, kěshì fàn hái méi hǎo.
(The cooking was done, but the meal was not ready yet.)
Ménsuǒ le, kěshì méi suǒ shàng .
(I tried to lock the door, but I could not lock it.)
In these two examples, the verbs ‘zuò’ (make) and ‘suǒ’ (lock) are two Activities having no endpoint or goal. Put in the perfective aspect ‘le’, they only express realization and termination of the actions named by the verbs, rather than indicate the attainment of the goals. So they allow the conjoining of a clause that negates achievement of the results.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.