Record sounds fuzzy in "busy" sections, but clear in others

Was listening to a copy of Yes "Close to the Edge" last night. Used record in very nice condition, cleaned before listening, and playback was very clear with low surface noise for most of the record. However playback got fuzzy and unclear in sections where the record got loud and more sonically 'busy' - notable when pipe organ was playing, and the more instrumentation that got added, the fuzzier it got. In all other sections it was nice and crystal clear - both before and after the fuzziness. I have not noticed this issue with other records, but I don't have any that have pipe organ or this many layers of instrumentation at one time. Behind this album, my most sonically busy is probably 'Dark Side of the Moon'.

What is likely culprit of this? What should I do to fix it?

Turntable is a Rega Planar 3. Not sure about cartridge/stylus. This was a holiday gift from my dad, and I gather it is a new high-quality stylus. Player rests on cinder blocks on floor of slab basement. I balanced the tone-arm and adjusted it to 1.8 grams tracking force, but I did not weigh it to confirm the calibration dial was accurate. Ordered a scale that should be here Tuesday.

Google searching seems to point to the most likely culprit being tracking force too low.