This is what I did: .... My account was back to it's old self - showing no expiration date. I called in for the umptiest time on 12/30 and was told the miles would in fact expire the next day.
Since I am currently 16 hrs ahead of W-Coast time, I had plenty of time to prep and was able to make a flight booking and transfer the rest (about 48k) to my IHG (hotel) account, in MHO the best transfer possible.
The transfer went smoothly, completed within 24 hrs and the ER account is showing 0.
Good riddance and a great clean-up start for the new year - I feel good about it :D

Say what? How do you transfer to IHG? I'd be all over that...

Due diligence .... just read my prior post ;)

Ah, thanks, but not interested in taking that big hit. Appreciate the response however.

Just got off the phone with them. I told them the details, and said that it appears this problem is well documented and widespread (said I googled it and found many complaints from others). I told the CS agent that since it was their mistake, I expected that they would reinstate the "expired" miles with the previously-shown expiration date in February 2016, and asked if he could do that.

Yes, it took 30 minutes to get to speak with someone, but after being transferred one time, I ended up with someone who (more or less) acknowledged the problem, and (after another 15 minutes on and off hold) said he would have the miles re-instated and the expiration date previously shown (in February 2016) restored within 24 hours. No runaround, no pushback at all.

So, it appears they will Do The Right Thing. As long as that does happen, I will be pleasantly surprised. Will keep my fingers crossed and check tomorrow. Will update this thread with the results.

About 10 hours later, just checked online. Miles have been restored. ^

Now, time to stir the activity/accrual pot...

My complaint through BBB resolved the issue. My miles were restored to the account.

Looks like the website no longer shows specific expiration dates. Now displays this:

"Expiration: 6 months from last positive accrual."

Now if only the search function worked properly you might be able to figure it out for yourself.

Same issue
 

I'm having this same issue with my husband's account. He had ~35k miles that in December the website said expired March 18, 2016. I went online 2 weeks ago to start planning travel to use the miles, and his account says 0 miles. He called and was told the policy switched from 18 months to 6 months of inactivity. He was told if he flew within two months they'd reinstate the miles. That is total crap as they are his miles and this is their error to just take them and not notify us of the change. :td:
It sounds like you've all gotten your miles back with a phone call or BBB compliant. I guess we'll call again and hopefully get someone else. Any other advice? I don't have a screenshot from December, though we do have a statement from September (I know, old) showing the miles value and March expiration date.

Call back. Be reasonable, but firm, and lead the call.

FWIW, it was never suggested that I needed to fly with them within 2 months. That's BS.

Here's how I approached it:
When I ran that by an agent, he just asked for the account info, what miles I was supposed to have, and put me on hold (off and on) for a while. He finally came back and said the miles would be re-instated within 24 hours. They were.

I suggest you try the same approach: here's what happened, here's what I expect you to do, can you do that now please? be polite, but firm, and give them an opportunity to do the right thing. I was prepared to escalate to all sorts of things, but that wasn't necessary.

Good luck.

I had the same problem with Frontier. I had over 88,000 miles that they said expired in February and they were gone. I called Frontier and got the response longleaf got. I then complained to BBB. BBB was great. The miles are back in my account.

Update!
 

Short version: Miles (supposed to be) reinstated within 24 hours!

Long version: Called Frontier and I was told the exact same thing as last time (his miles expired b/c 6 months of no activity, we could fly within 2 months to get them back). I threatened BBB complaint, the lady passed me on to her manager. Manager said exact same story as the first lady, I threatened BBB complaint, she talked w/ her manager, and now they're promising miles will be reinstated within 24 hours. She said I'll have two months to use them (which amazingly is the EXACT same date that the stupid website told me for months on end was the date the miles would expire...March 18, 2016!!!). So I asked if his account online would say that date as the expiration date, and she said 'no, it'll say six months from last activity'. Ohhhh their website is so functional and helpful! Ha! Then she said 'so that will be sometime in April'. What in the heck is she talking about?!?! How is two months from now April? I don't know, but I'm booking travel tomorrow and closing this account. Thanks for the help.

I cashed out my miles today for hotel vouchers. I can't trust these people.

Cashed out my miles 4 days before what I assumed was the *real* expiration date. I knew the exact day I had flown with them and that date, plus 6 months was to be January 20. Found that at Points.com I could use my 9,160 miles for a $25 gift card.

Six month expiration is completely stupid. I have no miles with them now. My family all had their miles expire (they didn't have enough for even a free gift card).

With no miles to "support," I have just one fewer reason to ever fly with them again. Combine that with the fact that these $19, $29, etc. fares are "sucker" fares, because you have to upgrade them with "the works" to make it even marginally decent to fly with them. Its almost always cheaper at Southwest.

Further, you can earn miles a number of different ways with Southwest (Chase Sapphire, Chase SWA Card) and the miles/points will actually be *useful*. With fast expiration, I can't see the point of getting a Frontier MasterCard.

Somebody in the company must have either read or written the book "1001 ways to screw your customer and make sure he never comes back."

If Spirit is your primary competition, maybe this makes sense. But, when Southwest is your primary competition, this is just bad marketing and bad business.

If they are around in 5 years, I will be totally amazed.