My bike is a Bianchi Virata from the early 1990's. Ultegra 8 speed groupset. I put new cables and a new chain on last year and ride 3 times/week in the spring, summer and fall. No issues whatsoever this season until 3 weeks ago. On a ride in mild rain I felt that the chain was not running smoothly then it snapped. So I had a new chain installed professionally (Performance Bike did the work). All was well. I had about 150 miles on the new chain with no issues and suddenly on a ride today it snapped. Shifting has been crisp. I have no idea what is going on and can't believe that relatively new chains would break just on their own.

Please let me know your thoughts.

What make and model chains and have you evaluated the failure points?

Shimano chains. Not sure of the model. I have not evaluated the failure points. I don't have either chain.

Any chance the lbs will warranty the chain?

I'll ask. I still have the receipt. Which by the way has the model number of the chain: HG-93.

So it probably uses a press in pin? I switched to quick link after I had an LBS installed pin fail. I'd take it back and have them fix it.

OP states he doesn't have the LBS installed chain.

The number one reason I've seen dozens of chains break is from the outer side plates working off the pin's end. This can happen from poor assembly (if the chain is assembled with a pin that gets pressed into it) and from poor shifting techniques. Yes other reasons happen but these two probably cover 98% of the causes. So when approaching a LBS about whether they miss installed the chain not having the chain in hand makes the question pretty much impossible to figure out. As in the evidence has been erased. Perhaps if you were told about how the first chain broke it might lend some light on the second one. But the OP also states he doesn't have that one either, was it with the bike when the second was installed?

It will be interesting how the LBS handles this with no real evidence. If the Op is a regular customer and has a good relationship with the shop then regardless of the exact why the chain broke (and the extension as to who's responsible) the shop might just eat the cost and install another chain at no cost. If not then it might be a test of how much the shop wants this customer to play nice on social media.

The take away is to keep the broken parts if you want to figure out what happened. Andy

Yes. I'd say it's a very high probability the shop didn't install the connecting pin correctly. If they choose not to cover the cost of another chain, you can pick up a KMC X9 chain for about 13 bucks and it comes with a quick link. Pretty easy to install yourself if you have a chain pin tool. Hopefully the shop will cover it, but it's always a good idea to keep any parts that fail that could be under some kind of warranty.
I made a video on how to size and install a new chain that may be helpful to you if you choose to install another chain yourself. FYI on average, a chain should last 1000-4000 miles depending on your size and riding conditions. If everything is installed correctly, it's pretty rare to see a chain break, but they all wear out.

The HG-93 is a 9-speed chain so if the OP reused a standard pin that could explain the failure. He did say the second chain was installed by a Performance Bike shop and they should know better.

A lot of the new chains seem to have swagged pins from the factory. IMO pins once pushed out should never be put back in. Get a new chain of the proper length and use a quick link.

Does anyone on the forum have any true information on these new style swagged pins.

Every make of chain from 9-speed on up uses swedged / rivited pins that should never be partally pushed out and reused.

Also
Check drive train alignment, bent crank/cog
Put it in a stand & watch for wobble, excessive side stress.
Front / rear derailleur damaged, bent ......?

Riding conditions excessively dirty ? Chain well lubed , clean , maintained ?

I've had had (and seen) quick links fail too.

When I first built my Cargo Bike, I put on a pair of Bell chains (needs to be LONG). Broke the chain twice in early testing, and that chain came off.

I replaced it with a Shimano 9s chain which worked, but wore out too quickly. I now have a Shimano 8s chain on it.

Anyway, don't buy just the cheapest chains you can find. Get a good chain.

Here's a follow up. I took my bike back to the LBS yesterday and they replaced the chain at no charge. They even refunded me the installation charge for the first chain, the one that broke. I asked what they found with the old chain (which I retrieved on Sunday) and they said they should not have installed a 9 speed chain on an 8 speed drivetrain. I'm no expert but from what I've read that shouldn't matter. It's moot anyway. The new chain is an SRAM PC850 8 speed chain.

Probably doesn't matter that it was a 9sp chain but they may be looking at liability issues if it could be shown that it wasn't the mfr. recommended chain and somebody got hurt. Could be other reasons such as they goofed the installation or who knows??? But, in any case they corrected the problem as well as refunded the labor so good on them for that and good customer service IMO.

AC&F in walled lake?

I believe that the OP mentioned Performance Bike did the work in post 1. Good for them to keep their customer. Andy

My fault.
didn't know there was one there.

As mentioned, Performance Bike in Novi. Across I-96 from Twelve Oaks Mall.