When Captain Picard and Data approach Counselor Troi's quarters, the door indicates "Lt Cmr Deanna Troi". She had already been promoted to Commander by this time.
While having been a male cat in most appearances, Spot is female in "Genesis." She was already shown as a female in Force of Nature (1993), but this time the cat's female sex is crucial to the plot.
In S6E16 "Ethics", we see various portions of Worf's anatomy. Including his back and his feet, both of which have Klingon ridges. At approximately 12 minutes and 17 seconds, Worf is running through his quarters in his pajamas and his feet are bare. There are no ridges like they had previously. They are regular human feet, not Klingon feet. At 12 minutes and 23 seconds, we get a very good look at Worf on bent knee and his left foot is in the middle of the frame, toward the bottom. There are no ridges on the top of his foot.
When Picard and Data return to the ship, they discover Counselor Troi in her quarters and leave her in her bathtub. Later on, when they go to Data's quarters to work on a way of reversing the "de-evolving" virus, Worf is trying to break through the door to get to Troi in the sickbay. How did she get there? Data and Picard didn't bring her there, and she couldn't have gotten there on her own in the condition she was in.
Worf's venom can apparently melt through the floor but it does not dissolve Picard's hand when it spills on to it.
Allowing for the possibility of de-evolving, it would not have been possible for Barclay to become an arachnid (spider). Because the evolutionary branch leading to spiders and the branch leading to humans had already split. You would not be able to de-evolve into something that was never on your branch. As a comparison, Troi becoming amphibian would be correct, as amphibians are included in the early days of the human branch.
When Data and the captain return from recovering the torpedo from the asteroid belt, the Captain orders Data to adjust the shuttle's attitude to match the Enterprise before they land. This is a pointless command; matching speed, orientation and rotation of one ship to the other would be part of the normal approach and landing process, and would not require a separate command.
Again, once on-board the Enterprise, he issues direction to Data, and states that he, himself, will take care of the 'attitude' of the ship. There is no up or down in space, and the attitude of a ship is meaningless unless measured in relationship to another object. Gravity is created artificially in a local environment on board the ship. There is no reason to adjust the 'attitude' of a single ship in open space.
A large amount of the biological "information" in the story is wholly bogus.
After Data and Captain Picard encounter Riker in his de-evolved form, Data mentions that he believes Riker's current de-evolved state to be Australopithecine. Appearance renderings of Austrolopithecus recreated by experts looks much more like a modern primate and in no way resembled Riker's state of devolution, a detail that Data could not have possibly missed.
When Data and Picard are in the shuttle and they locate the Enterprise, Data says that it is 2 light years away. How can the small shuttle they were in make a trip of 2 light years when the shuttle is incapable of warp speed. Even at low warp the trip would have taken years. Later in ST:Voyager Resolutions they reveal that the type 9 Shuttle had the top speed of warp 4.
In Conspiracy (1988), Admiral Quinn picks up Geordi and throws him throw a set of closed doors with the doors easily being knocked off their hinges. But in this one, the devolved Worf bangs on them for a long time and can't budge them while only denting them.
Geordi states that seven security teams are searching for Worf because the sensors are having difficulty locating him. However, when Worf is shown later, he's still wearing his combadge. Since Data uses Ogawa's combadge to find her, there's no reason as to why Worf's combadge couldn't be used in the same way to track him.
The shuttle craft Picard and Data used to retrieve the wayward torpedo was somehow able to traverse 2 light years in a very short amount of time when it found the Enterprise on sensors. Without warp capabilities, it would have taken the shuttle many years to get to the Enterprise, and even at a modest Warp speed, it still should have taken several hours or days to do so.
When Picard and Data find Troi in her quarters and Data scans her, he tells Picard that "she is no longer human", but Troi never was entirely human; she's half-Betazoid, which is why she's got some degree of ESP. Knowing how exacting and technical-minded Data is, it doesn't make sense for him to say this line as if Troi is a normal human.
During the conference room briefing immediately after Dr. Crusher has been wounded and placed in stasis, Nurse Ogawa is sitting in for the medical department. But in the preceding scene (just before Crusher's injury), she tells Ogawa to call for Dr. Selar and another doctor, both of whom would be senior to Nurse Ogawa. One of those doctors would be in charge of the medical department in Crusher's absence and would be in the briefing.