"Unsaved Changes" remain forever

Hi.
I have a TL-WR841N router, with OpenWrt 18.06.1 and from today I have issues with any change of configuration.

I try to change any settings and click "Save & apply" as usual, but the change isn't saved and in fact it temains only added to the list of "Unsaved Changes".

I thought it can be a problem of insufficient memory, but in System -> Software I see 56 KB (16%) of free space.

I think this means that there is still space to save configurations, right?

What could be the cause of the failed rescue?

Thanks in advance.

Very likely not enough free space. Getting below even 256 kB can cause problems (due to how jffs file systems work).

https://openwrt.org/supported_devices/432_warning

See, for example,

Thanks jeff.

I'm using also the package "travelmate" and "luci-app-travelmate" so the memory remained was not enough.

Now I have downgraded to LEDE 17.01.5 but, without having installed travelmate yet, I see 208 KB of free space.
I understand that it is still too little.

Do I definitely have to give up using this router with travelmate?

Adding packages to a build is usually better than adding them to the overlay, as the build compresses the package. It sounds like you'll have to really be careful with what you install on that device and might need to strip more out, such as PPP and variants. (Typically "no LuCI" would be the first step, but I'm guessing that would defeat the point of travelmate).

You might look through the support thread to see how others are managing this