CC Madhya 6.91
īśvarera māyā ei — bali vyavahāra
“Despite directly perceiving the symptoms of the Supreme Lord in the body of Śrī Caitanya Mahāprabhu, you cannot understand Him. This is commonly called illusion.
Gopīnātha Ācārya is pointing out that Sārvabhauma Bhaṭṭācārya had already seen uncommon symptoms of ecstasy in the body of Śrī Caitanya Mahāprabhu.
These uncommon symptoms of ecstatic love indicated the Supreme Person, but despite having seen all these symptoms, the Bhaṭṭācārya could not understand the Lord’s transcendental nature. He was considering the Lord’s pastimes to be mundane. This was certainly due to illusion.