"There is X" vs "There is a/an X"
Solution 1:
It really does come down to mass nouns. Putting an article in is more specific and you can then quantify rather than generalise.
Taking reluctance as an example, if you can specify a reluctance then it is "a reluctance". "A reluctance" cannot signify more than one reluctance. If you say "there is reluctance" (without the article), that could mean there is more than one reluctance. So they are certainly not exactly the same in meaning.