What is the lifespan of a SIM, and what would symptoms might appear with a defective one?

I recently had an iPhone problem of an intermittently unresponsive screen.  It would work for a few minutes, then simply stop responding.  After waiting for a few seconds up to a minute, the screen would respond normally again, then stop responding a bit later.

Under AppleCare+ the phone was replaced.  Before being replaced, diagnostics were run which showed only an issue with the battery.

The replacement iPhone showed no problems at first, then identical symptoms began on and off, then more frequently, then after only a few days the new phone was virtually unusable.

As the likelihood of two phones having identical hardware issues was astronomical, I began looking for a common cause.  The original phone had been totally wiped clean and reloaded from scratch, first from a backup, then as a new phone.  Each time the symptoms returned.  I went through the same process with the replacement,  with the same results.

I searched for iOS issues, thinking a bug in iOS 12 was the cause, but found nothing similar.  Noting iOS 11 had major problems, perhaps this was an offshoot.  Then thinking perhaps some data related to my AppleID was corrupting my phone, but this seemed unlikely as my iPads weren't affected.

I finally ran across the issue of SIM viruses.  Since the SIM was the only commonality between the two, this seemed like the only possible remaining cause.  Yet this seemed as unlikely as anything else since the SIM was over a year old, and I use only a couple of apps and rarely share data with anyone or even chat with anyone.  Where could a SIM virus possibly have originated?  Besides, such infections are very rare anyway, and are almost always introduced in a new batch SIMs at the factory.

My local Apple store gave me a replacement SIM free of charge, as is their policy with all iPhone owners.  (Yes, in case you didn't know, anyone can get their iPhone SIM replaced free from Apple!)  Then on my way back to my car it hit me...   What if it isn't a virus, but simply a defective SIM?  

Now that seemed like a real possibility, and it did indeed turn out to be the actual cause.

Googling for info on defective SIMs yielded nothing useful.  There is also no information on the anticipated lifespan of a SIM.  So I researched SIM manufacture, and discovered they are simply a microchip on a thin piece of PVC (vinyl), similar to current credit cards, only much more cheaply made because they aren't expected to endure any sort of stress in their day-to-day use.

The chip itself is unlikely to fail since it simply provides data, and the contacts are gold coated, so oxidation seems an unlikely cause.  The vinyl might degrade a tiny bit, but not enough to warp or have any significant effect on performance.  So a chip degrading over time seemed unlikely until I remembered the adhesive used to bind the chip and vinyl together.  Adhesives break down rather quickly, especially cheap adhesives.  So what might be the effect of deteriorating adhesive on the back of a microchip?  What symptoms might it produce?  The most likely symptom would be a slowing of the phone, as it repeatedly attempted to retrieve data from the failing SIM.  It could theoretically slow it down a whole lot, depending on how the phone interpreted the data fault.  Slow down processing of the whole phone, or just an app, or simply the response to a touch of the screen.  In the case of a friend of mine, her failing SIM caused her phone to regularly show that a new device has just logged on to her AppleID, requiring her to verify it!

Until recently, the majority of people replaced their iPhones annually, and probably got new SIMs in the process.  But technological advances have slowed, so replacements are currently averaging two years or more.  Now many people replace them only when they're not working well—slowing down or behaving unreliably.  I now can't help but wonder how many problems are caused by their lowly worn-out SIMs.  Most average people don't try to diagnose their phones, they simply assume they're worn out and need replacing.

P.S.  Now that Apple is replacing physical SIM cards with internal hardware, will their iPhones be even more reliable, lasting even longer?  Will Apple's stock continue to decline because of continued sagging sales of iPhones not wearing out?  Will Apple try to make their iPhones not last so long (planned obsolescence) as when they removed MagSafe from their Macs?  Inquiring minds want to know!!