Saw someone had this issue as well.

Have a Synapse 5, can't express how much I absolutely love the bike.

Even the stock seat fits me! Which is super rare

Have one issue though, when im on the smaller cog up front, 3-5 gear have a small issue. When im climbing a hill, the chain seems to be slippng somewhere. As I put pressure on the peddle the chain would go slack a bit and then a second later it feels like it re engages the teeth. Issue is, this makes me very nervous when I am hill climbing while standing up. It makes me feel as though I'll fall when my feet are at the 12 position and pushing the pedal down with my weight.

When I shift to the bigger cog in the front, all my gears work with no issues. No slipping. Whats going on?

Maybe your rear indexing is off a little. Can you tell if it's slipping on the cog or actually jumping cogs?

Was the chain recently replaced?

It may be that your pedal stroke is sufficiently uneeven that you're engaging and disengagin the freehub: i.e. you surge forward, then effectively coast for a fraction of a second. Thus you have to rengage the pawls of the freehub as you press down on the pedals.

The harder gear in the big ring, pulling more chain per revolution would make that less likely, which explains why it only happens in the small ring.

The chain can't just slip; if it's not adjusted and skipping, it would make a lot of racket and you'd know it.

It's possible the pawls in the free hub are sticking and it's not engaging and the freehub is slipping.

It's also possible the cassette is catching on the spokes, and interfering with the freehub working properly.

I don't think the chain was recently replaced. At least to my knowledge. This bike was bought brand new from a LBS on saturday.

TBH, I felt this while doing a test ride in the parking lot as well but I chalked it up to maybe it needing in a break in period but even at the slightest incline, gears 3, 4, 5 seem to be having issues.

No matter how much pressure i put into first gear, it have the sensation Im describing. This "slipping" feeling.

My stroke is pretty uniform or I should I say i try to keep it as uniform as possible.

I'll try to record a sound clip or something. Hopefully I don't fall while holding the phone and peddling.

This is the first time something like this happened so me so tbh, I can't tell which is which.

This is what is great about buying a new bike from your LBS. Take it back to them, show them what it is doing, and they'll fix it.

Right. It could be any number of thing. Take it back to the LBS and have them check it out.

BTW, I once had a similar problem. It was because I didn't join the chain properly. The chain skipped and jammed in the chainstay on a steep climb. I ended up with some serious scratches.

inspect the chain very closely, if its in good shape you probably just need to make a minor adjustment, take it to the LBS you bought it from, have them show you how to do that adjustment and get on your way.

another resource, Sheldon Brown-Bicycle Technical Information odds are you can find your problem and how to make the adjustment yourself very easily if you have even mediocre mechanical skills.

Here is a clip of what I am referring to, for those that are interested.

Vocaroo | Voice message