I see this as well on my Win10 GTX3070 host. The Amicable exe gets its dedicated thread while CPU BOINC crunching uses other threads set by ProcessLasso. Most tasks are 3:33 or about and then others spike way up to 10x as long. I saw one running yesterday that had very low GPU usage.
https://sech.me/boinc/Amicable/results.php?hostid=215172

@[AF>Le_Pommier] Jerome_C2005 you assumed correctly I am using Windows. Thanks for your steps the only thing I have to do differently was use command prompt instead of power shell to get it to run.

I am not sure why it took so long to run in Boinc. Will put it down to something within Windows. As you can see from output below at ran in a smidge under 3 minutes, right where it's meant to run on my card :-)

16:22:23 (18576): Can't open init data file - running in standalone mode
Initializing prime tables...done
C:\Users\User\Documents\GitHub\Amicable\Amicable\Amicable_OpenCL.cpp, line 1118: OpenCL platform available: NVIDIA CUDA
C:\Users\User\Documents\GitHub\Amicable\Amicable\Amicable_OpenCL.cpp, line 1134: Using 'NVIDIA CUDA' OpenCL platform

C:\Users\User\Documents\GitHub\Amicable\Amicable\Amicable_OpenCL.cpp, line 577: Self-test passed
16:25:14 (18576): called boinc_finish(0)

Thankyou for all the help along the way I appreciated it

Yes PowerShell is a shell/terminal same as good old cmd.exe from windows, the purpose is the same.

Good you could make it :)

I'm not sure to understand the concept of running amicable "standalone", so the "127658160073" in the launch parameters = the details of the task that would receive from the project and run ?

Yes PowerShell is a shell/terminal same as good old cmd.exe from windows, the purpose is the same.

Good you could make it :)

I'm not sure to understand the concept of running amicable "standalone", so the "127658160073" in the launch parameters = the details of the task that would receive from the project and run ?

I ran a task in standalone mode because I wanted to see how long it was going to take to run, when I ran the task on Boinc it took 12 minutes where it should have taken around 3 minutes. in standalone mode it did take around 3 minutes

My question was more : since you run it standalone, how can it be that "127658160073" is the only parameter needed to feed "all the data to the task" ?

In other words : when ran via boinc as a task, the only parameters sent to boinc to run the executable are "127658160073" ?

My question was more : since you run it standalone, how can it be that "127658160073" is the only parameter needed to feed "all the data to the task" ?

In other words : when ran via boinc as a task, the only parameters sent to boinc to run the executable are "127658160073" ?

I have no idea

Parameters are "/lpr 127658160073 127658185709 /task_size 200102005550" and they set the range of primes to check, and the total amount of checks to perform (for progress reporting to BOINC client).

Thanks I appreciate the insight as to how it works

Thanks for clarification Sergei.