If you're having problems with a specific router, if there isn't a thread for that device, you can start one and get some help on "putting your firmware on a diet." There isn't going to be any "magic" solution for devices that simply don't have the required resources for a full build of current, robust OpenWrt firmware.
For 850re v2 check my post at the end of this thread:
Not as good as an official openwrt release but works with enough free space left to save a few configs.
@jow Now that several devices have been reported here that lose configuration after a reboot, what are we going to do now with those devices?
Since we know that they don't work as expected with 18.06, I propose to take the respective 18.06.* images offline, and suppress 19.07 image generation (or take them offline after generation, whatever is easier to implement).
What do you think?
I agree with that. Do we already have a condensed form of the devices listed here?
Sure, here is what I could exctract from this topic (and other topics that are linked to this one):
This posting is wiki, i.e. everybody can edit it for adding more affected devices.
Please make sure to only add devices with 4MB flash.
Devices with 8MB flash are not affected and shall not be added to this list.
Unfortunately no idea, how to edit the previous post:
A further failing 4MB flash device is:
Edit button at the bottom right of the post. Just added it for you.