The Add Limit Reasons to Log File option is automatically checked on the newer TS versions. That is why you cannot find it in the Options window.
In the far right column of the log file you will see XPRO show up. This stands for eXternal PROCHOT which is another name for BD PROCHOT. ThrottleStop is detecting this while gaming and it is also recording a very subtle drop in CPU speed. Some of these drops are only lasting for maybe 0.1 seconds so it is probably not even noticeable while gaming. ThrottleStop uses high performance timers in the CPU so it can detect tiny changes in the CPU multiplier. On screen data while gaming is not as accurate. If this sensor continues to glitch out and get worse, you are definitely going to be noticing these drops to 800 MHz. That is what happens when BD PROCHOT is activated.
If you want the MHz drop to be a lot more noticeable in the log file, try turning on the More Data option on the main ThrottleStop screen. This changes the CPU sampling frequency to 8 times per second instead of once per second. If you do this, the CPU multiplier drop in the Multi column will be very obvious. Post another log file of that.
DATE TIME MULTI C0% CKMOD CHIPM BAT_mW TEMP NVIDIA GPU VID POWER
2020-05-07 06:48:58 39.92 69.0 100.0 100.0 0 83 1770 71 1.1049 37.0
2020-05-07 06:48:59 39.86 70.4 100.0 100.0 0 84 1770 71 1.1177 37.8
2020-05-07 06:49:00 38.00 78.9 100.0 100.0 0 87 1875 71 1.0988 39.9 XPRO
2020-05-07 06:49:01 34.50 86.0 100.0 100.0 0 83 1875 71 1.1111 40.4
2020-05-07 06:49:02 39.89 74.0 100.0 100.0 0 84 1740 71 1.1123 39.5
2020-05-07 06:49:03 39.93 72.7 100.0 100.0 0 84 1740 71 1.1138 39.2
2020-05-07 06:49:04 39.68 77.7 100.0 100.0 0 85 1755 71 1.1028 40.8
2020-05-07 06:49:05 39.93 74.2 100.0 100.0 0 85 1755 71 1.1118 39.7
2020-05-07 06:49:06 40.00 75.4 100.0 100.0 0 86 1755 71 1.1023 40.5
This section of the log file during an XPRO event shows the average multiplier go from approximately 40 to 38 to 34.5 before recovering back to 40. It might be subtle at the moment but it is definitely happening.
Long term, I would leave the BD PROCHOT box unchecked in ThrottleStop. It is not necessary. Your CPU will still thermal throttle if it ever gets too hot. Disabling BD PROCHOT does not interfere with this.