The keep all in the feed setting just specifies that ti should keep
them if possible. if you want to stop a file being auto deleted then
you can mark it kept in downloaded files> select file> keep.
Check you have reserved enough space in setting download settings. so
there is enough space allocated to keep all the files you would
normally use at once.
Otherwise you would have to uncheck update automatically this would
stop auto downloads.
There has to be something like this as your sdcard would keep filling
up which would also be annoying.
best
rb