What's the difference between “no strict construction” and “contra proferentem” clauses in contracts?
The expression "no strict construction" provides some flexibility regarding the compliance with the contract. The parties may depart from the literal language of the contract as long as their departure does not defeat the purpose or intent of that contract. Unless prescribed differently, the principle of "strict construction" would equally constrain the conduct of all the parties to the contract.
Contra proferentem disfavors only the party who drafted a contract. The doctrine is applicable where the language of a clause is simultaneously consistent with reasonable interpretations which would lead to opposite outcomes.
The rationale behind contra proferentem is that the party who drafted the contract is presumed to outweigh the counterparty in terms of bargaining power. Thus, the doctrine seeks to somehow compensate that disparity in bargaining power whereas there is no element of compensation in the principle of "[no] strict construction".
Note that the excerpt you posted in regard to contra proferentem is contradictory. By definition, contra proferentem entails a disadvantage to the party who drafted the provision at issue. Instead, the first sentence in the excerpt should state something in the sense of "No contra proferentem" or "Invalidation of contra proferentem".