I feel the OP’s pain, despite being tubeless for nearly ten years, it can be a very frustrating exercise.
Last weekend, I had six goes at getting a tyre to seat on the rim. Each time, the tyre deflated almost immediately. I must have gone through three reels of electrical tape, but the issue was the sealant I was using – it wasn’t viscous enough to slop around the inside of the rim and seal a tiny gap in between the rim tape and the valve.
Back to the OP – Electrical tape should be stretched as it’s wound round the rim. I’ve even seen a freshly inflated tyre force the electrical tape to bulge into the spoke holes and force a puncture. There’s no sealing that, it’s a case of starting over and salvaging as much sealant as possible. If you’re using the correct rim tape, then this should be less of an issue, unless the tyre bead is forcing the tape to bunch up and is exposing spoke holes.
When tubeless goes pear-shaped, it’s an absolute massive bellend.