There are have been posts explaining why it's not possible.
De-select ARP from your project list.

I avoid the swapping tasks issue by running only one project at a time. I know that there are those who like the set and forget approach but there are a few projects where that really isn't a good idea. ARP on wcg is one. I don't know enough about other wcg projects to answer for them. CPDN is another and one which makes the size of tasks for ARP look small.

ARP1 app checkpoints at 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%.

A few possible problems I can guess if tasks fails to stay in background.
1. Limited RAM or BOINC configration RAM setting, when too low, will kill task in background and not keep in memory.
2. Switching task too frequently. try changing the configuration to 2880 minutes for scheduling period switch task.

Options, computing preferences, switch task every 2880 minutes, use 100% RAM.
Or open:
Linux Debian: /var/lib/boinc-client/global_prefs_override.xml
Windows: C:\ApplicationData\Boinc\global_prefs_override.xml

<global_preferences>
<cpu_scheduling_period_minutes>2880.000000</cpu_scheduling_period_minutes>
<leave_apps_in_memory>1</leave_apps_in_memory>
<ram_max_used_busy_pct>100.000000</ram_max_used_busy_pct>
<ram_max_used_idle_pct>100.000000</ram_max_used_idle_pct>
</global_preferences>

BOINC tools, read local pref file, or run: boinccmd --read_global_prefs_override

It is possible to set RAM to 200% in config file which I did to my intel atom N270 2GB just to get both Rosetta tasks to start.

Use a large enough swap file or swap partition so the task doesn't fail on 100% RAM usage. This can sometimes slow down a little. Do note that if virtualbox is used, virtualbox memory cannot go to swap and can run out of memory.