Forge 40.2.9
firstaid-1.11.1.jar
secondchanceforge-1.18.2-1.5.0.jar

Second chance does not activate when First Aid is installed. I assume it's because first aid changes how the health system works.

I've just tested with those exact versions and it worked flawlessly for me, "oof" sound and all. I think you may have something else going on.

For the record, I tested by activating second chance, setting difficulty to hard, and spawning a creeper directly on me. When the creeper exploded, I heard the sound effect and survived. To make sure it wasn't just survivable, I went into the config and turned off the Second Chance feature and repeated the process. This time I died immediately.

Let me know if this still isn't working for you and we can troubleshoot the real issue, otherwise I'll be closing this issue.

It may be an incompatibility with another mod since I have not tested with only those 2 mods. I didnt think it would still work so I will try and figure out the cause.

I've just tested with those exact versions and it worked flawlessly for me, "oof" sound and all. I think you may have something else going on.

For the record, I tested by activating second chance, setting difficulty to hard, and spawning a creeper directly on me. When the creeper exploded, I heard the sound effect and survived. To make sure it wasn't just survivable, I went into the config and turned off the Second Chance feature and repeated the process. This time I died immediately.

Let me know if this still isn't working for you and we can troubleshoot the real issue, otherwise I'll be closing this issue.

So I tried again with only second chance and first aid installed and although I heard the "oof" sound, second chance did not in fact, activate. The simplest method I used to test this was using fall damage and enabling it in the config.

Edit: I tried again using a lot of creepers including a charged creeper and this time second chance has indeed worked with the "oof" sound. Maybe some config options do not work as intended with first aid?

If it works at all with first aid, it should work with everything I'd think. I looked at how first aid handles things and it lets all other mods handle damage first and then deals with whatever is left. Could you try it without first aid? Although if you hear the oof sound that would imply it's working on its own... strange that second chance wouldn't activate with it...

I'll play with it more myself tomorrow and let you know what I find

Second chance for fall damage does work. Maybe it doesn't after a certain height? I will try testing this

Yep, second chance activates but the player still dies if they fall from a tall height

First aid may not necessarily be precise about how many damage is taken, causing a bit more health lost / bringing a critical body part to 0 and killing the player