In a sentence like:
It allows us to overcome problems such as sparseness and/or cold-start
, which of and/or should be used?
When using such as, you mention the items regardless of their probability, availability, ordering, or any other criteria. The other important point is that there may be other items subject to the situation, but it suffices (or you prefer) to utter only some of them. Because of this, in many academic papers are seen expressions like:
such as item1, item2, and item3.
In your case, if you mean "It allows us to overcome both problems and nothing else" I prefer such a structure:
It allows us to overcome sparseness and cold-start problems.
An example from Collins Dictionary:
The fruit and other foods such as meat, fish and eggs boost serotonin.
The sentence above uses such as because there are (many) other foods that boost serotonin, but the author doesn't want to list all of them.
There are many dangers in the desert such as snakes, scorpions, and heat stroke.
In this case you use "and" because all of your examples are present in the desert.
You will pick a book for your book report such as Moby Dick, 1984, or Brave New World.
In this case "or" is correct because you are only choosing one item.
In cases where an unknown number of the example items will be present, you can use "and", "or", or "and/or" (read as "and or").
In Yellowstone park you may encounter a variety of animals such as bison, bears, wolves, and/or moose.
The "and/or" construction is less technically correct, but it's reasonably common and it's useful if you want to emphasize that the examples listed are independent but not mutually exclusive.