Thank you so much Sean! Yes, you are right! The issue was related to the RAM, but also the CPU. When I changed the default settings in RStudio Cloud from 1GB RAM to 2 GB RAM, and from 1 CPU to 2 CPU, it worked just fine with two collaborators. It still did not work even with the max RAM possible without increasing the CPU. Basically, the default settings for RAM and CPU work fine for 1 collaborator, but for more than 1 collaborator we need more RAM and CPU. It would be useful to have some guidelines about the optimal RAM and CPU usage for different number of collaborators. The fact that real collaboration in RStudio Cloud does work well with several collaborators, using the appropriate RAM and CPU, is really great news though, and I'll start using the collaboration feature immediately. Thanks again for the prompt response and for resolving this issue for me!