In the end, I could solve it by following the recipe from the Arch Wiki:

• Boot into Windows
• As an administrator, run powercfg /h off
• Shutdown Windows

I also changed /etc/fstab to a UUID to refer to the NTFS partition, after a first attempt failed, where I did not use the powercfg command but disabled it by clicking through the GUI. Not sure, why using a UUID should make any difference (in the Wiki, it is not explained further). But at least it is working again.

Source: Arch Wiki (NTFS-3G: Metadata kept in Windows cache, refused to mount):

The problem is due to a feature introduced in Windows 8 called "fast startup". When fast startup is enabled, part of the metadata of all mounted partitions are restored to the state they were at the previous closing down. As a consequence, changes made on Linux may be lost. This can happen to any NTFS partition when selecting "Shut down" or "Hibernate" under Windows 8 or 10. Leaving Windows by selecting "Restart", however, is apparently safe.

 

To enable writing to the partitions on other operating systems, be sure fast restart is disabled. This can be achieved by issuing as an administrator the command:

 

   powercfg /h off

 

You can check the current settings on Control Panel > Hardware and Sound > Power Options > System Setting > Choose what the power buttons do. The box Turn on fast startup should either be disabled or missing.

 

If you cannot mount your NTFS partition even when following this guide, try using the UUID instead of device name in /etc/fstab for all NTFS partitions. Here's an fstab example.

In the end, I could solve it by following the recipe from the Arch Wiki:

• Boot into Windows
• As an administrator, run powercfg /h off
• Shutdown Windows

I also changed /etc/fstab to a UUID to refer to the NTFS partition, after a first attempt failed, where I did not use the powercfg command but disabled it by clicking through the GUI. Not sure, why using a UUID should make any difference (in the Wiki, it is not explained further). But at least it is working again.

Source: Arch Wiki (NTFS-3G: Metadata kept in Windows cache, refused to mount):

The problem is due to a feature introduced in Windows 8 called "fast startup". When fast startup is enabled, part of the metadata of all mounted partitions are restored to the state they were at the previous closing down. As a consequence, changes made on Linux may be lost. This can happen to any NTFS partition when selecting "Shut down" or "Hibernate" under Windows 8 or 10. Leaving Windows by selecting "Restart", however, is apparently safe.

To enable writing to the partitions on other operating systems, be sure fast restart is disabled. This can be achieved by issuing as an administrator the command:

   powercfg /h off

You can check the current settings on Control Panel > Hardware and Sound > Power Options > System Setting > Choose what the power buttons do. The box Turn on fast startup should either be disabled or missing.

If you cannot mount your NTFS partition even when following this guide, try using the UUID instead of device name in /etc/fstab for all NTFS partitions. Here's an fstab example.