Sometimes you just fall out of love with your gel polish and go through a period when nothing goes right and you start to doubt yourself.
It's difficult to get your mojo back. I had this problem at the beginning of the year and I was seriously thinking of changing brands. we went through all of the issues you describe, falling out of love with the colours, worrying about technical issues, thinking our lamps were to blame, posting question here...
So, from the top, OPI is a great brand, clients love it and you've invested in the correct lamp. Why change? I suggest you invest in a proshaker in case your gel pigment has settled at the bottom of the bottle. OPI France and Belgium are distributors for the proshaker, I think the UK distributor is out of stock and not planning on ordering in any more at present - I've been trying to buy a proshaker for some time.
Clean your lamps (safely) with surgical spirit and glass cleaner spray. Adjust your service to suit the physicality of clients. I find that clients have more and more issues with their hands nowadays - all that texting! I usually just do 4 fingers of one hand at a time and the thumbs together. If you have one, you can put a second lamp on your desk and have one for each hand.
My method is prep both hands ready for painting. Then take a hand, base coat 4 fingers and cure, paint 2 fingers and flash for 10 secs, paint next 2 two fingers and cure whole hand. Repeat with 2nd/3rd coat and top. Some colours need flash curing more than others and some nails are more affected by gravity than others so I don't flash cure every colour and every client. Repeat for other hand.
Then paint the thumbs, pick up the lamp and hold it at chest height. Get the client to make a loose fist with her thumb on top of her curled fingers, place her thumbs together and then slide her thumbs into the lamp nice and level. I bob my head around making sure the thumbs are under an led and not rolling sideways. I caution the client explaining that the gel is affected by gravity.
If they really can't control their thumbs I buff off and start the thumbs again individually, holding the client's thumb in position. Usually clients hate this so much that they insist they can do it after a couple of coats and amazing - Yes they can!
It is very much about taking charge of your client. They need to be involved with the treatment and not treating you like the invisible nail fairy.
Once I'd put myself back in control of my nail reputation we resolved our issues. We've all agreed as a team that we don't need to change gel brand.