Bubble tips are very finicky and no one really knows for sure how or why they do/dont bubble up. Some are bubbled up for months but then never again. Some are always bubbled up. It just depends on the nem. Even 2 nems from the same mother in the same tank can produce totally different bubbling behavior.
Just keep everything in check and stable and you have nothing to worry about.
29g Mixed Reef, 150w 14k Phoenix MH w/ Moonlights, Reef Octopus BH1000 HOB Skimmer, Ecotech Vortech MP10es, ReefKeeper Lite (Plus), PH Probe, Temp Probe, ATO, Carbon/GFO Reactor.