I used to have a issue where my joy-cons would disconnect randomly in handheld mode. Seems like other people also had this issue.
Described here:
https://www.reddit.com/r/NintendoSwitch/comments/a26skn/joycon_disconnecting_while_connected_physically/
It seems like there was NO physical damage with the joy-con clamps/hooks. My joy-cons would snap into place (with a little wiggle horizontal and vertical).
My fix for this:
I assumed my problem was with the electrical connection, not position issue.
I just blew into the electrical connection on both switch and joy-con. Seams to work perfectly now. Probably just dust buildup.
Simple, but not instantly obvious solution.
Hope this helps someone!
by Sharp_Pressure8921