Huh? As of 2016-08-12, the Best Service downloads page for Engine still shows v22.214.171.124 as being in beta, and says, "Please be aware that this version can still contain some bugs." The beta has been available since 2016-05-11, so it's not news that it exists. If you click on that download link, you really do get the beta installer, so if you have the previous version and it's working (and you don't want to take a chance on the beta version), stick with what you've got until Best Service releases the final version.
As of this writing (2018-05-03), the Best Service Downloads page for Engine shows "Installer Mac OS X 126.96.36.199 - 10.9 - 10.13 (64-bit) - AU & VST & AAX Native (Pro Tools 11+)", but the listing is not an active link. There's no way to download the v188.8.131.52 update. What's up with that?
It is written "Coming soon". I think that it is clear enough. It is an announcement, simply. It is not yet totally ready. Even on this present KVR page they have not changed the current version number from 184.108.40.206 to 220.127.116.11. And that, even if they write "Aktuelle Versionen" on their webpage.
Conclusion : the version 18.104.22.168 is about to be released, but not yet. We simply have to still wait a bit. That's all. Let's wait. In the meanwhile I don't have any great issue with the version 22.214.171.124.
Actually, in the way it's written on the Best Service Downloads page, the "Coming soon" is shown for the Windows version, whereas the Mac version explicitly lists the relevant system versions and formats.
And I'm not sure how your browser is displaying this page, but mine very clearly shows that v126.96.36.199 is the current Mac version as of 2018-04-30. In my experience, it is not customary for Best Service to update the Engine version on this page before they actually release it, so my query is not unreasonable.
As for version 188.8.131.52, you might not "have any great issue" with it, but your experience is not universally applicable. Version 184.108.40.206 takes a long time to load the plugin and even longer to load or change an instrument in Logic Pro 9 running in macOS 10.12.6.
Yes, of course. But probably that the best is to ask them directly by their support. I have already used their support (for one of their products) just last year, and they replied immediately, kindly and in a very reactive way. You should try, you would have obviously their actual answer to this point which is, I perfectly recognize it, is troubling.
I did contact support immediately after I posted here, and I received a reply today. Apparently the release has been delayed, although they didn't say why.
That still doesn't explain why they would list 220.127.116.11 on their downloads page and also show it here as the current version before it's actually available, but it does eliminate some uncertainty. At least it's a confirmation that it's not a question of someone having forgotten to include a working download link.
For the record, I agree that Best Service's support has always been very responsive, helpful, and professional. I certainly have no complaints in that regard.