Plesse issue following commands and post their outputs. These outputs will show which version of dump1090 is using your dongle.
pgrep -af rtl
pgrep -fa dump1090-mutability
pgrep -fa dump1090-rb
EXPLAINATION
Your setup requires the rbfeeder's builtin "dump1090-rb" to start when rbfeeder is started. Once "dump1090-rb" is started, both the rbfeeder and fr24feed get data from it.
It seems that on reboot, the fr24feed started before rbfeeder could start and start "dump1090-rb". The fr24feed when did not find any dump1090 rumning, it triggered installation of "dump1090-mitability" which captured the dongle and started outputing data on port 30005. The FR24 therefore working properly using this data. However since Radsrbox is set to use its internal dump1090-rb, fails as its internal "dump1090-rb" has no dongle left to use and gives "rbfeeder[603]: rtlsdr: error opening the RTLSDR device: Device or resource busy".
SOLUTION
If output of any of the above noted 3 commands "pgrep -fa xxxxxx" contains "dump1090-mutability", then do following:
In file /etc/rbfeeder.ini, under [client], change "network_mode=false" to "network_mode=true".
Then restart rbfeeder OR reboot Pi
The above modification will set rbfeeder to get data from dump1090-mutability port 30005, same as fr24feed is doing.