Been noticing a lot of issues with Synergies lately, especially when playing my tank since I try to activate those as often as possible. I mention Templar abilities a lot here since my wife plays a Templar Healer and these happen a lot when playing together.
First issue is sometimes it's really had to activate a synergy. For example Templar's Spear Shards (and any morph) and Sorcerer's Lightning Splash. The X prompt doesn't show unless you are in an exact correct location. So I have to button mash and move around it a lot to activate it.
Second issue is when there are multiple synergies possible. Good example here is if a templar drops Cleansing Ritual (or any morph) and drops shards, the prompt with toggle back and forth rapidly between the two, making it nearly impossible to activate them. It also plays the sound affect for being able to activate a synergy each time, so you hear it about 2 times per second.
Third issue is an order of importance one. If Templar drops Nova, Clensing Ritual and Spear Shards. It will keep toggling which one to activate. In reality a person would most likely want to activate an ultimate's synergy over anything else. So Ultimate's should take precedence over other synergies.
Fourth issue is the activation itself. I notice this mostly with Lightning Splash. If I activate the synergy with my Stamina Tank, the damage for each enemy it is in the 1-2k range. If I do it on my magicka sorc or templar, it's in the 5-6k range. I feel like synergies like this should base values off the caster who cast it, not the one who activated it since the caster is most likely magicka/spell based (in this instance) and as Stam Tank, my magicka and spell damage is very low, so it does almost no damage. I just find that on my tank it's almost useless to activate that synergy since the damage is so low. I can more than that with light attacks.