This problem has been happening on console for almost a year now. Mostly in pvp, but also happens in dungeons playing solo. Sometimes my regen will stop for 2-3 ticks and then all of a sudden I will get all my 2-3 ticks at once. That's bad enough, but other times it will stop for more then 3 ticks and when that happens I never get my resources back until it eventually it starts to regen again. Very frustrating.
I have never had any problems for 4 years (yeah once after an update a few years ago) and now it happens again in Cyro after an update. Mana is drained in no-time. Please take a look @ZOS_GinaBruno
Pretty hard for ZOS to look into this without any information. Would help ZOS if you explained a little bit of the type of fighting you are in where this is happening for example. Could be as simple as enemy players using poisons to reduce your magic and regen. It will help if others are also having the same issue and start posting information here.