A number issues to consider here.
Firstly, NATO ISR are not some magical all-seeing eye, and are subject to the same limitations of range, endurance, availability, geography and weather as everyone else’s. Not even bring in decoys, deception, jamming and good old fashioned camouflage etc.
Range and time are probably most relevant here because thus far, NATO ISR has always operated from neighbouring NATO countries’ airspace or international airspace. Never Ukrainian airspace. As the battlefront moves further east, that degrades the capabilities of the bulk of NATO ISR operating over NATO member states.
As with all live battlefield intel gathering operations, you will never get a complete picture from one or even several passes of recon satellites or recon planes. The successful Ukrainian offensives were made possible by relatively static frontlines that allowed NATO to gradually build a comprehensive picture over weeks or months. The current far more fluid situation massively degrades the completeness and accuracy of NATO’s battlespace awareness and understanding, especially under constant time pressure due to the need to continue pushing ahead and not loose momentum
ISR are most effective at spotting big things. Big columns of troops and armour are next to impossible to hide, but troops dug into defensive positions, especially in or around population centres, are far harder to accurately and comprehensively assess. This is one of the reasons a lot of NATO and Ukraine fanboys are getting their undies in a twist about Russia evacuating civilians - it makes it much much harder for NATO space based ISR to get a good understanding of what’s going on. Are those buses and troop trucks leaving town full of civilians or soldiers? Are the same trucks and buses coming back empty or full of troops and supplies? Not impossible to tell of course, but hard and eats up finite and precious analytical and recon assets’ time and bandwidth.
In the past, it was Russia that was struggling with this when they were on the offensive, and their big troop concentrations were very obvious and easy to find and track by NATO ISR. But now it’s the Ukrainians who are on the move, so the burdens have been flipped and even Russia’s bare bones ISR should have little trouble finding and tracking the bulk of the Ukrainian forces while NATO ISR now not only need to track the retreating Russian forces, but also assess and map out defences of new frontline settlements as well as keep tabs on Russian reinforcement.
Also worth considering is that even with perfect tactical battlefield awareness, it is still possible to be lured into untenable strategic level positions or even traps if your supply lines become overstretched and bad weather hamstrings the mobility that was key to your current successful strategy.
All of this is also assuming that NATO has Ukraine’s best interests at heart, and are not at all swayed by domestic considerations and demands and are above using Ukrainian blood to buy domestic political capital. I mean that’s totally unprecedented and it’s not like the US President has been conducting foreign policy, economics policy and managing the US strategic oil reserves with the upcoming midterm elections as the main and only consideration.