170-190 hits for kurios certainly is "grossly low"; I just did a lemma search from the Browse window on it in BW9, and got 9322 hits in the entire Greek Bible. I also tried the lemma search on prostethēsetai from Matt. 6:33, and got 325 hits.
I suspect there may be some settings that haven't yet been set right in your new BW installation. My first suspicion is search limits, which would account for the low number of reported hits. Click on the little row of green and/or yellow blocks just below the Command Line, and then click on Choose Search Limits. See if that setting is restricted to some limited range of books.
Search limits, however, ought to produce the error message "No matches were found but you have search limits set. You may want to turn them off" if you search for a word that is not found in the range of books in the search limits setting. The "the following word or form cannot be found in the current search version" message resulting from a lemma search is very strange, since the search version for lemma searches should default to the morphology text for the appropriate language. Nevertheless, it can't hurt to check what search version is actually being set. Do a search that fails in the way you describe, and then click on the downward arrow at the right end of the Command Line. This will drop down a list of recent search terms. The highlighted term at the bottom of the list should be the one you just searched on, and it should be something like BGM .προστίθημι. If it's not BGM, or if the lemma isn't what it should be, that would indicate the problem, though I have no idea what could be causing it.