Intermittent no start/no click?

New to me the vehicle listed above SR5. I drove without issue for 3 weeks, then it sat for 1 week. Came back to accessory dash lights and then silence when the key was at the "On or Start" position. I've started from the top and have worked my way backwards trying to find the issue because now it's intermittent. Initially, I inspected the fuses and relays. Did the park-neutral-park game with no luck. Chose to replace the Starter relay.
Battery and cables were charged and intact but did install an additional ground. I beat the starter then replaced it but it was found to not be the issue. Swapped the ignition switch with no change. Changed out the neutral safety switch and at last she fired right up. This is where the issue went intermittent. Never shuts off while in motion and it's a guessing game whether I need to wait 10 minutes for her to start again or 30. I will do nothing but wait. Could it be a heat sensor? What's not talking? No aftermarket alarm that I can find but as a newbie it hard to exactly identify everything. I have a multimeter and am at your mercy! Thank you