Why does Undo stop working in Illustrator CC 2017?

Question

Design

I draw a mobile application. Artboards - 30-40 (add-delete), layers - 5-6 pieces, file ~ 90 mb (compression, PDF-compatibility, implementation of links and color profile - everything is disabled).
CTRL+Z stopped working. Moreover, saving also behaves strangely - when saving, the asterisk in the file name disappears for a second, and then reappears. If you close the document immediately after saving, it will prompt you to save, as if you didn’t just press CTRL + S just now.
How to be? Configuration:
Win 10 x64 PRO
processor Intel Core i7-4790, OEM
motherboard MSI H97M-G43
RAM DIMM DDR3, 8GB, Crucial
HDD 1TB, Western Digital Caviar Blue,
WD10EZEX free)
graphics card MSI Gaming GTX 960 4gb