I personally have x3 Sync cards with no issues. But then, I also don't mash the cli button for padding limits I'll never use at least 30% of per 1 to 3 months to justify said limits.
As others mentioned already, I think the cld's start happening for 2 different reasons. Reason 1 is when Balances are carrying over on multiple cards and only the minimum payments are being made (best to pay 3x+ minimum payments on carry overs imo). And reason 2 is cli requests on multiple in network cards that are not getting remotely close to at least 15% Utilization within a 1 to 3 month period.
They make their money off the business swipe fees and interest charges. So if you don't swipe enough, spend enough, or pay enough on a high limit card, those are funds that can be relocated to someone else that makes them more money at a lower risk of default.
In perspective, a high limit on a card someone doesn't appear to be able to afford large spending on or only pays the minimum on could equate to a future maxed out default and loss for them. So it's really a matter of loss prevention when a cld happens.
In my opinion anyways.
I currently have 4 trade lines with Sync and over the years they never closed or CLD my accounts! Unless the CC was discontinued or moved to another bank (Marvel, Walmart).
Sync has many CCs that they are easy to get, easy to grow... However they do not like to be used for utilization padding. As long as you recognize that, then you should be fine. Keep what you like and cancel what you have no use for.
Verizon CC is good card and maxes out at 20K
Lowes can grow very high limit, but I would not push it.
Amazon not hard to get, but I prefer the Chase version.
Sync is not inquiry sensitive so you can app for couple of them, however other banks don't like credit seekers these days! Just keep that in mind.
I only have 1 Sync card and that works well with my profile which is the Verizon VISA card It's only used for my family's cell phone bill. Who needs a 20k credit limit for a cell phone bill that is a couple hundred a month? Not me but I appreciate the padding that it affords me on my overall utilization. If you treat them well and don't go overboard with approvals on their products, constantly asking for a CLI before it's time, running up the utilization without significant payments, or constantly late on payments, doubt they would say BOO to you.
but that's just my opinion
I've had zero issues with Synchrony going back to the GE Money Bank days. I had a couple of cards closed years ago after years of non-use but those were one-time purchase accounts (for example, buying a Sleep Number bed 20 years ago was one time too many). I have $68.5k in combined limits between Lowes, Amazon, PayPal Credit (formerly BillMeLater), and Synchony Premier MasterCard (formerly Rakuten Visa), which is comparable or below what I have from most of the major credit card issuers (American Express, Bank of America, Chase, US Bank). Nearly all issues we've seen with Synchrony have been major red flags with creditworthiness, too much too soon, or extremely lopsided credit profiles (i.e. revolving credit consists of $100,000 on 15 Synchrony cards and a $300 Capital One card). In moderation, one should have zero issues with Synchrony.
There are very few stories (I recall only one actually) of a Sync CLD/shutdown that seemed "jumpy" to me.
However, there are too many threads that start out like- 'I was AA by Sync for No reason' but buried 14 mesages later, OP reveals that s/he has several cards that have been over 89% for months.... 
My DW and I have three Sync cards.
I have a mostly idle Amazon Store at $10000, am an AU on a her quarterly used Lowes at $35000 and DW just a got CLI on her frequently used TJX MC to $9500. Our past nine year Sync history has not been drama-filled at all.
IMHO, our Sync cards are actually on the low tech/boring side but they do execute very the specific {why we apped} purpose of getting back 5% on their spend.