As for your watch running 5 secs fast per day, you're within the specs, so that it is not a problem.
As for your 2d problem, yes, that is an issue.
I'm really sorry for you.
Did I have such experiences with my JLCs?
Only once in may whole JLC Collector watch, with an Amvox II, but it was perfectly fixed.
Wish you a better future with JLC.
Best,
Nicolas;
JLC is having some major quality problems, and I do not believe that they care to correct them. I had a problem with a MMC2 running 10 seconds slow per day. In addition, it did not fit well on the wrist as the case back to me is poorly designed. I returned it for a MMC1. You should expect excellence at the price you are paying. You would expect the 1000 hours test to be closer tolerance than COSC, but it's not....it's purely marketing.
Certainly JLC should rush this for you and at a minimum thow in a strap or 2. That to me would be customer service!
By the way, I own 2 JLC's, so I know of what I speak.
2 issues which were perfectly solved: One on the accuracy: It was running too slow, so I had to send it for them to set it, and one on a Vintage.
Yes, JLC has quality issues, as all the brands: a total lack of issues doesn't exist, in an human world.
Now, saying that JLC doesn't care to correct them is not true.
As for your watch runnig 10 secs slow per day, it is not a problem, if it regularly looses 10 secs per day. Every watch needs to be set after a while, as it depends on so many factors.
Just an advice: Every watch you consider should be tested on YOUR wrist before any final decision. We don't have the same wrist, and the real test may lead you to have different feelings.
Best,
Nicolas.