Ok, I think I have fixed what I suspect were the causes for both issues in latest CBSubs nightly build.
The second issue was (I guessed) this one
forge.joomlapolis.com/issues/8701 , also fixed in latest nightly.
Please upgrade CBSubs (backup, then CB Plugins->Install/Upgrade, then "Refresh" and "Upgrade all") to latest nighly build and re-test with the Paypal Sandbox.
Then if one of the two tests still doesn't work, I'll really need the information asked above for the corresponding issue.
If all is fixed, please reply too, just to confirm that both issues are now solved.