Apps launch way too slow when connected to wifi but without internet

Hi,

I recently found that when connected to an internal wifi (aka, a wifi without internet access). macOS behaves very slow and launching app be like 30~ times slower than it was normally, for some app.

example: safari, IINA, Movist

MacBook Pro (Retina, 13-inch, Mid 2014) on macOS 10.14.6

Any idea?