Windows Recovery Environment
One should be able to boot into WindowsRE by going to All Settings > Update & Security > Recovery and click Restart. If that doesn't work, there are any number of reasons for this, and you're not alone. In addition, the Recovery Environment should match the upgraded version of Windows 10 on your machine. I've had the same issue, and it took a while, but I did get it resolved.
After a couple of days of fruitless effort, I discovered that the following was fustrating my efforts at every turn to re-enable the Windows Recovery Environment, but for whatever reason, Windows does not offer any failure mode or error code. All I kept getting was the task "completed successfully", even though it did not complete at all.
This partition must be at least 300 MB.
The Windows Recovery Environment (Windows RE) tools require additional free space:
If the partition is less than 500 MB, it must have at least 50 MB of free space.
If the partition is 500 MB or larger, it must have at least 320 MB of free space.
If the partition is larger than 1 GB, we recommend that it should have at least 1 GB free.
When calculating free space, note:
The recovery image, winre.wim, is typically between 250-300MB, depending on what drivers, languages, and customizations you add.
The file system itself can take up additional space. For example, NTFS may reserve 5-15MB or more on a 750MB partition.
This partition must use the Type ID: DE94BBA4-06D1-4D40-A16A-BFD50179D6AC.
The recovery tools should be in a separate partition than the Windows partition to support automatic failover and to support booting partitions encrypted with Windows BitLocker Drive Encryption.
We recommend that you place this partition immediately after the Windows partition. This allows Windows to modify and recreate the partition later if future updates require a larger recovery image."
Those recommendations are for UEFI/GPT systems. I had 450MB with 51MB free space. So I should be good, right? After going through all the following (and some more problems that I created for myself along the way) it still wouldn't work. I used BootIt Bare Metal, did a little bit of shrinking, some sliding, and got my partition up to 550MB. Now it's all good. I guess a partition larger than 500MB doesn't actually need 320MB of free space. I've tried it a number of times and it just keeps working. Here is how it's done: