I remember a reference about improving the robustness of the scripts in Arkk with the next fractal release. Unfortunately issues with the bomb/Temporal anomaly remains.
At least for CM. In our case it seems that the issue was triggered because we phased Arkk into the Archdiviner while an anomaly was present. We killed the anomaly, the dome appeared but the bomb never went off since Arkk left and the Archdiviner appeared. Although i cannot be sure with the chaos the fight has, i think that is what triggered the issue. But do not quote me on that.
After that point the bomb/anomaly/dome in a sense de-synqed having constantly either the bomb never appearing even though there is an anomaly and someone getting the message or the other way around having the bomb without an anomaly. It is different than previously that the anomaly just stopped appearing. And this was retained for the whole instance and not only the current fight. This whole thing (if triggered) makes CM runs really problematic at this point.