I am posting this to help anyone else that runs into what happened to me. The other day our Whirlpool Dishwasher WDF520PADM7 showed a solid CLEAN light and a blinking SANITIZED light. The dishes were clean and all looked normal in the unit. (Mmmm, weird !?) The settings we use for our daily dishwasher run are Normal cycle with Hight Temp, SaniRinse, and 4 hour delay options. I started researching online, and must admit, by early information, that I homed-in on the idea it was a bad heating element. I found out how to run the internal Service Diagnostic Cycle which begins with a light display of the last stored error code. The error code displayed was 4 blinks followed by 3 blinks. When I checked the error chart the corresponding cause pointed to the washing motor. (Whaaaaat ? That went against my current mindset !) So, at the end of the Diagnostic cycle, which includes a short Heated dry period, I opened the DW up, wet my finger, and did a quick touch of the heat element. Oh yeah, it was sizzling hot, so it definitely wasn't the problem. So, I was back at researching the possible causes for a 4-3 code. I ran the diagnostic cycle again and paid close attention to the segment that involved the wash motor and all seemed normal. On one appliance blog, a tech suggested it could be something impeding the performance of the wash motor, like lots of gunk restricting the filter, or an object in the wash motor impeller chamber. First step wash to take out the filter basket in the bottom of the DW and clean it, then check in the filter-hole for any foreign material. So, when I took out my filter basket, it had a gunky film over all the screening material which I proceeded to clean off the warm water and a toothbrush. I reinstalled it and later that evening set up the DW for our daily run after we go to bed. The next morning I checked the DW and VOILA, it had a solid CLEAN and SANITIZED light. Problem solved !
Cost : Zero dollars $ + multiple hours research and testing.

Hope this helps someone in the future !
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UPDATE
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Well, following the wash cycle on the 2nd day, the sanitized light was blinking again, and when I ran the Service Diagnostic Cycle, I got the 4-3 code again. So now I am wondering if my wash pump is intermittingly having faults, or is it the control board not sending correct voltage to the pump. Time for some voltage meter readings during the wash cycle. I will return with my findings !

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UPDATE 2
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Well. before I went after this problem with my multimeter, I decided to do a cleaning cycle in NORMAL with the AFFRESH cleaner. After completing that, we set our DW up that evening for our daily wash.(NORMAL, HIGH TEMP, SANIRINSE, 4 HR DELAY, and NOT heated dry) The next morning the DW showed a solid CLEAN and SANITIZED light, and I said to myself, "OK, good, but what about tomorrow ?". So, for the last 6 days, we have been greeted with solid CLEAN and Sanitized lights, and clean dishes (just wanted to say that the dishes have been clean ever since the blinking sanitized light first showed up.) MY guess is the OWI was impeded with gunk, and the AFFRESH did the trick. So, we are going to put a monthly clean cycle on our DW's schedule.

Edited by user Tuesday, May 31, 2022 10:03:36 AM(UTC)  | Reason: The problem is solved