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I’ve also got this problem

Changing file ai_bp_reactions_dynamic_css.php to this:

<?php
header('Content-Type: text/css');
	
require_once( explode( "wp-content" , __FILE__ )[0] . "wp-load.php" );

	echo ai_bp_main_animation_css();	

?>

and function ai_bp_reaction_dynamic_style_init in class/class.php to:

function ai_bp_reaction_dynamic_style_init() {
	if(bp_current_component('activity') )
	{	
		wp_enqueue_style('dynamic-css',
                 esc_url(plugins_url('activity-reactions-for-buddypress/css/ai_bp_reactions_dynamic_css.php') ),
                 null,
                 null,
                 null);
	}				 
}

fixed it for me.

Only difference I notice is that the icons now animate in on hover.