To improve the performance of LHC@home projects, you can modify your BOINC client preferences using your BOINC Manager as follows:

• Under the Preferences Tab "processor usage", in the line "While processor usage is less than X percent (0 means no restriction)", you can at the beginning keep BOINC default for X is 25% which causes some pausing/resuming of the VirtualBox process. If you want to try to contribute a maximum, you can set the box X to 0 (zero).
• Under "Use at most X % CPU time", set the box X to maximum 80 % in the beginning, to make sure that your machine does not get blocked. (The BOINC default used to be 60%, but is now 100% for some client versions.) You can later try to set the box X to 100 % if you wish to contribute a maximum. 
• On multiprocessor systems, you can chose to use only a subset of them and reduce the number of tasks running in parallel accordingly.

BOINC Network preferences to suspend and resume work should now work properly.