I am finding that this POR sometimes allows reset to go high for up to 10ms when power is first applied.
Green is power being applied. Blue is reset going high for almost 10ms before being activated. This defeats the purpose of the circuit.

 

so what is the purpose of the circuit? i see only three components with POR activating SSR to let the data pass through.
you are not using POR as intended and the very unusual setup is problem likely only affect you. the SSR is not an MCU.

 

I have a battery that communicates with another device. It gets hot plugged into the device. the data line is also used for powering a single piece of logic. I did not design this!!! But I have to make it stop blowing stuff up. So when you first plug it in, you can get spikes up to 9V on the 5V line. My solution is to break this line and put in the SSR to slowly turn on the line. This is on the non-battery side. I was able to add a dedicated 5V to this board. This is an inline solution. I am thinking that I just need to build a old school POR circuit, R/C with a Schmidt trigger buffer. In this way I remove the pull up resistor for the SSR and have the buffer drive it.

 

I am thinking that I just need to build a old school POR circuit, R/C

Using a NE555 as a delay.
When 5V is applied to the 555 the SSR turns ON after a delay set by R1 and C1.

Another version using a mosfet.
Delay set by R1 and C1.

 

I will give these a try. I worry about NE555, because it may have issues with the hot swap and initial unstable GND.

 

I wouldn't worry about the 555.

 

I wouldn't worry about the 555.

NE555. Remember both power and GND is being hot plugged at the same time. When this is working at its best in this situation I get a 3v to 4v bounce on the output just as the hot plug happens. The SSR takes 40us to fully turn on and the bounce is just less than 2us. Unfortunately sometimes the NE555 is on for about 1.3ms instead of the bounce.

I will try the mosfet tomorrow. I will also look into why the SSR fixes my problem if delayed for a bit and it does not when turned on immediately.