There are 2 ways to pronounce this expression 1. ‘ de plu zen en plu ’ or 2. ‘ de plu zen plusse ‘, but a liaison at the end of the expression with the following word is not required regardless of which pronunciation is chosen. The latter pronunciation would be expected here though.

What may be audible here would be enchaînement - with ‘s’ (not z) of the 2nd ‘plus’ transferred to the start of the first syllable of the following word starting with a vowel/h muët. This is not always easy to detect for the non-native ear, I must say !

(Note that this is a positive expression of ‘plus’ so the 2nd use of ‘plus’ can definitely be pronounced ‘plusse’. The negative expression of the word ‘plus’ is never pronounced as ‘plusse’.)

Remember only a limited number of liaisons are obligatory. As a ‘general rule’,  there is less frequent use of optional liaisons in everyday speech, as it can sound quite formal in modern French. 

Link to an answer from Cécile to a related question : 

https://progress.lawlessfrench.com/questions/view/the-pronunciation-of-plus-in-de-plus-en-plus-in-the-last-example-j-ai-de-plus-en-plus-de-mal-a-me-co 

https://www.lawlessfrench.com/pronunciation/required-liaisons/ 

https://www.lawlessfrench.com/pronunciation/enchainement/