Issues with replacing/updating files in tableau

Question

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I'm a new tableau user, so please bear with me as I try to formulate my question.

I just ran my 1st set of monthly reports this week and there were a lot of reds and exclamation marks that came up that I noticed we had to manually fix. My coworker, who is also new to tableau, has just gotten used to fixing these errors but I'm trying to figure out why it is the same issue for every single file we are uploading into tableau. Basically, we are replacing/updating about 13 reports every month with new data in Tableau, but it's just not a smooth and automatic process as in the YouTube videos. We are having to go back in and either replace references or Tableau is trying to find a link between the reports or some calculation field is invalid.

To my understanding, all of this should update automatically as long as we have the same info (fields) each month, right? My coworker is fine just fixing those errors every month but there's gotta be a way to actually automate this process. My coworker also said that tableau is very glitchy. A way of saying that is just the way it is with the software, which I have a hard time accepting. This thing costs my company $800 per person!

All we are doing in Tableau is replacing the previous months reports to get new numbers. Also, we are taking over someone else's work in tableau so could it be that the original file had a different set of data and that is why we are having all these errors come up each time we're adding the new data? At this point I'm trying to see if I can just recreate last month's tableau report and add this month's to see if we still get those errors. Is that even possible? So can anyone recommend any videos on things that can go wrong when replacing a file in Tableau? Does anyone have a suggestion on what to do? While YouTube is very helpful, most don't cover issues that might come up when replacing a file, except for replacing references or fixing a calculation field. Thank you so much for your responses!