I can indeed replicate the issue using the first 3 triggers on the list. The fourth does not happen.
The fifth issue (related to the scrollbar), I have seen it before, but does not replicate as easily, perhaps its just my opinion, but I find it would be more convenient if each component remembered the position the scrollbar was left at, instead of always going back to the beginning, but that its a different matter.
That being said, I do not think that what is happening to me is related to the 5 known triggers, it happens when I am working on the timeline of "large" assemblies (300 + bodies). What I refer to as traversing long timelines.
As part of my workflow with Bommer, I often go back on the timeline to change parts (for example changing a screw for one that is used in other parts of the assembly to reduce BOM items, etc), As well as restructuring components so that they export a hierarchical BOM in a way that makes sense for assembly. This involves rolling back the timeline and roll it forward step by step while making changes, going in and out of components. And at a certain point the marker disappears.
Perhaps it has something to do with working on multiple screens?, I am constantly going between screens on my Win10 computer (laptop screen + hdmi screen + usb screen), sometimes I find that after going between screens, the right-click context menu starts showing up on the main screen while Fusion is on the HDMI. Perhaps that can also be a clue? Once the contextmenu thing happens, it also requires a Fusion Reboot
I will continue to look for more specific ways to replicate it, however as @wjatevrr mentions, once it happens the workarounds, or replicating the 3 triggers, do not bring it back. The only way to get the marker back is to reboot Fusion.
Thanks and I hope this can be corrected.