I'm a Insider member since Oct 2014, get all the builds till the official launch of Windows 10 last July.
A few days before the official launch my Windows 10 TP (build 10240) had a boot problem and gave me a UEFI boot error, since the Insider Program was locked and I can't get any Insider Preview build to work I had format my PC and install my Windows 8 Pro and follow the upgrade path to Windows 10. (Reserve a copy, wait for the update and install the Windows 10 (Pro) and activate with my valid Windows 8 Key, no hassles there.
After success upgrade I went to Security and Updates > Windows Update > Advanced Options and hit the Get Insider builds > Get Started button, restart my PC and check if Fast Ring was selected and it was. Last month it came out Build 10525 and later on Build 10532 and I didn't receive any of those.
I tried to force the download by hitting constantly the Check update button on Windows Update, but the only thing my Windows Update download is Windows Defender definitions. So, I tried the following: in Advanced Option, I hit the Stop receive preview builds, restart PC and go there again I hit the button Get Preview Builds, restart again and wait a few days... no luck.
Since I don't had any luck there I post some questions in Microsoft Answers and report the problem, a few days later receive some answers, but none of the those answers worked out and one of them seems to me a bit stupid, so the suggestions was:
1 - Uninstall any anti-virus. (don't have any, so it really doesn't apply to me);
2 - Safe Boot with Network (did that, produce no effect what so ever);
3 - Selective Startup with all services stopped except Microsoft services (same as above, produced no effect, still didn't get any update via Windows Update);
4 - Create a new Administrator account and run the Windows Update from the new account (although might work I found this solution a bit awkward, I mean, I have to create a new account with Administrator privileges and then subscribe to Insider Preview Program with that account and then make all the process, I did it, no effects also, bit I thought that was the dumbest solution ever... );
5 - Drivers update - (All my drivers are up to date, some from the manufactures, others from Microsoft, no hardware problems, so can't anything about that);
6 - Reset IP Address - (Did that, nothing happened);
7 - Windows Update as Trusted Sites - (Did that, nothing happened);
8 - Change DNS to 184.108.40.206 and 220.127.116.11 - (Did that, nothing happened);
So in total despair I contact Microsoft Answer Desk by Phone, and after a few minutes trying to explain what is my problem (I'm a portuguese from Portugal and ours Answer Desk is provided by Brazilians which don't quietly understand us - Brazilian Portuguese is quite different from European Portuguese) the woman gave me this solution:
Re-install my Windows 8 Pro and from there wait that Windows Update give me the Insider Preview update, and if Windows Update tries to install regular Windows 10 upgrade, she said to stop the upgrade and differ that update and wait for the Insider Update...
I didn't make this yet because I'm hard to believe that will work. I mean, in Windows 8 I will get the Windows 10 Insider Preview as an update? Last I checked I had to install Windows 10 TP with an ISO and boot from that ISO to get started and the new Insider Preview program state that I only have to set Windows Update to Get the Preview Builds (which I did) from a Windows 10 activated install (which I have).
By the way, my Windows 10 is set to USA as location and has the display language set to US English, I had also set a Portuguese keyboard setup, set my region to Portugal and Proofing tools are setup to US English and Portuguese (Portugal). I'm stating this since if my display language is not supported by Insider Preview I don't receive any builds (Portuguese currently not supported).
So please help me understand why I'm not getting the Insider builds and I'm still stuck in build 10240...
Here is a screenshot of my Settings and my Insider Hub:
Here is a screenshot showing that my Windows Update service is running, in this screenshot I had change the Ring to Slow and wait a day and change it again to Fast, that was a suggestion from someone in Microsoft Answers, no effect whatsoever: