The receiving record for 2nd class postage is simply not good enough, a lot of mail goes missing. There is no way of proving it of course, but I suspect it is given very low priority, hence the bad service.
If you are sending something that stands a chance of getting to it's destination on time, then 1st class is how it should go. The other alternatives include electronic mail [email] and texting
It is I'm afraid just another cost that increases. The PO have given it their thoughts and added to the cost!
Brian