Is the DeepScreen scanning Atlantis.exe or the actual .rtf file ?
Putting C:\Program Files (x86)\Atlantis\Atlantis.exe in the DeepScreen Exclusions is unlikely to resolve this if DeepScreen is actually scanning the .rtf file/s. That exclusion would exclude C:\Program Files (x86)\Atlantis\Atlantis.exe when it is started up, but it doesn't exclude its actions, opening the .rtf file is an action of Atlantis.exe.
Something that you could try, from the avastUI > Settings > Antivirus > Hardened Mode - set that to Aggressive. As strange as this may seem it could reduce this problem.