Question: why is my relationship level not increasing from 40? Any tips will be appreciated
If by "unlock door event" you mean that you have to unlock the door before the night starts, then be sure to familiarize yourself with this article: https://rec.miraheze.org/Suspicion as this will help you reduce suspicion - no more lockpicking doors
Dev added some event related to certain amount of relationship, which currently for only 20 and 40 work as a must do before you can progress, those are:
20 - cooking together*
40- running date*
60- couch groping*
80- shower scene* and kitchen bj
100 - wake up sex, kitchen missionary, (0.4.3.4) forest prone bone
The * means you have to view them all in order to get the wake up sex scene