No, not my first time seeing this phenomena.
Actually, while it is rare, because I hear from thousands of customers spanning across all the different boards and online communities, I have seen it a few times (including some of my own personal items over the years).
It is simply when oil was hot from manufacturing process, air in the vial is expanded, and then the vile is sealed; when the air cools its pressure drops causing a vacuum which on rare occasion pulls strong enough to distort the septum inward (suck it down) and create a divot.
The inward pulled septum does not effect the product nor sterility at all -- if still sealed, it is no different and totally safe to use.
I have personally used mine like this without issue (other than a little annoying to try to wipe with alcohol before drawing; i simply wipe with alcohol soaked cotton ball and press it down against divot hard enough so I can contact all the surface while I rotate the vial -- then, divot has alcohol in it which takes longer to dry -- that is the annoying part).
Other customers have used theirs too without issue.
Just like with a normal flat septum, you have to make sure you get it wiped and have alcohol in the divot to sterilize outside surface each time and let completely dry (the annoying part because of the divot) before each draw.
However, none of the other customers nor myself have ever experience any oil leaking.
If you see evidence that the seal is compromised, I would not use it.
IF this is the case, please contact customer service via the "contact us" form on the basicstero site and explain what you have including an details of a leak.
I do not have the authority or ability to address the issues beyond that advice (I have no access to orders/account or ability to ship anything) so please contact the company and take things from there. IF the contact form does not allow pics etc, maybe you can include the link (url address -- just click little post number in the top right corner of you post and then copy the address to that exact post) for your post here on MESO to show more details.
Code:
https://int.basicstero.ws/index/contact
I hope all that helps you brother