Enemies glow is not related to this. The main problem are those 1k enemies and AOE damage - game needs to search for enemies in range of each explosion and handle each of them.
Try to turn off particles (though explosion particles were greatly optimized in 1.6.0) that may help a bit but the main reason will still be there - not every device is capable of handling explosion mechanics on thousands of enemies, I see no ways of optimizing that part of game other than reducing max amount of enemies on map.

Hi. This problem is an event that can happen to everyone. ☺

I think the only solution is the Settings. Enter game settings. turn off some features.

as an example: Freezer tower; slows down enemies. but this event keeps a lot of enemies and slows down the game. This is very natural. Think like the GTA 5, the higher the graphics of the game, the slower the game frame rate, and even that depends on your in-game activity. The more you play this game, the more the game has to freeze.

Do not accumulate too many enemies to solve this event, albeit a little bit, improve the towers according to the wave of the game, use the freezing towers properly, avoid the use of various towers and do whatever it takes. this is the solution. Have a nice day ☺

May get fixed with season re-balancing in one of the future updates