If behavior is the same when skipping local tracks and the queue clear helps then this might be a sign that your platform reaches its limits. An upgrade to a more capable platform for Roon Server may be your best choice but please don’t pull the trigger based on my sole opinion. Try to get some opinions from other users with similar or bigger libraries as well first. Also try to project your future needs (what is your expected library size in 3 years, 5 years, …).
Roon seems to have a bit of a performance problem right now, especially for users with bigger libraries (50k+ tracks). The team seems aware and is searching for a solution but there is no time-frame currently and we also don’t know how much of a relieve a solution may present.
Also your search issue is likely unrelated to your current hardware and upgrading would therefore don’t help with that.