I was facing with this problem nowadays. Camera is a 2CD2041G1-IDW1 with the latest v5.5.88 firmware. It refuses connection to the HikConnect server on WiFi. With wired, it's OK. It was strange 'cause I've installed the same camera some 2 months ago and it was working fine. The working camera's firmware is v5.5.82.
v5.5.88 Release Note states that HikConnect is not supported via WiFi anymore on DS-2CD1X43G0, DS-2CD1X53G0, DS-2X41G1-IDW, DS-2X51G1-IDW, DS-2CD2X47G3E, DS-2CD2047G1, DS-2CD3X41G0 cameras. Talking to the distributor they claim that there were hardware changes as well so no way to downgrade without bricking. I don't see any point in this, one more irreducible hit from Hikvision but gotta live with it.
If you need this function do not upgrade your camera!
v5.5.88 Release Note states that HikConnect is not supported via WiFi anymore on DS-2CD1X43G0, DS-2CD1X53G0, DS-2X41G1-IDW, DS-2X51G1-IDW, DS-2CD2X47G3E, DS-2CD2047G1, DS-2CD3X41G0 cameras. Talking to the distributor they claim that there were hardware changes as well so no way to downgrade without bricking. I don't see any point in this, one more irreducible hit from Hikvision but gotta live with it.
If you need this function do not upgrade your camera!