I should say the following first. I have found a workaround, on Mint Cinnamon, for lid close not suspending the laptop. (I think that I found the workaround somewhere on this forum.) The workaround consists in enabling one of Mint’s settings. That setting is the one, in the Settings window, that enables suspension-on-lid-close even when an external device is attached (even though I had no external device attached).
Still: I have had, and continue to have, on Mint, a problem similar to that which Pierre reports on Ubuntu. Here is that problem. Upon suspend, or perhaps it is upon resume, the computer reboots. (Pierre reports that a reboot happens ‘a few seconds’ after logging back in. In my case, the reboot is in progress as soon as I have lifted the lid.)