What would cause Google Apps Script to hang on GetSheetByName?

I managed to get this to happen with the simplest possible code:

function test() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  Logger.log("before");
  var st = ss.getSheetByName("STATUS");
  Logger.log("after");
}

Results in:

Head    test    Editor  Sep 21, 2020, 7:07:32 AM    3.087 s 
Running
Stackdriver logs
Sep 21, 2020, 7:07:32 AM    Info    before
Sep 21, 2020, 7:13:32 AM    Error   Exceeded maximum execution time

This all started when this function:

function updateSheets() {
  var ui = SpreadsheetApp.getUi();
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var st = ss.getSheetByName("STATUS");
  var filelist = st.getDataRange().getValues();
  var dt;
  var folder = DriveApp.getFolderById(uploadID);
  for (i=0; i<filelist.length; i++) {
    var iter = folder.getFilesByName(filelist[i][0]);
    dt = new Date();
    if (iter.hasNext()) {
      var file = iter.next();
      st.getRange(i+1, 2).setValue(file.getLastUpdated());
      st.getRange(i+1, 3).setValue(dt);
      var name = getSheetName(file.getName());
      var data = Utilities.parseCsv(file.getBlob().getDataAsString()); data.shift();
      st.getRange(i+1, 5).setValue(data.length);
      var sht = ss.getSheetByName(name);
      if (!sht) {
        ss.getSheetByName("MASTER").copyTo(ss);
        sht = ss.getSheetByName("Copy of MASTER");
        sht.setName(name);
      }
      sht.getDataRange().clearContent();
      sht.getRange(2, 1, data.length, data[0].length).setValues(data);
      sht.getRange(1, 1).setValue(file.getLastUpdated());
      dt = new Date();
      st.getRange(i+1, 4).setValue(dt);
    }
    else {
      st.getRange(i+1, 2).setValue("File Not Fount");
      st.getRange(i+1, 3).setValue(dt);
      st.getRange(i+1, 4).clearContent();
      st.getRange(i+1, 5).clearContent();
    }
  }
}

with this the sheet STATUS

File    Last Updated    Start Time  Finish Time     Lines
Classes.csv 9/19/2020 5:00:09   9/21/2020 5:51:18   9/21/2020 5:51:20   1842
Customers.csv   9/21/2020 5:00:05   9/21/2020 5:51:20   9/21/2020 5:51:22   950
Items.csv   9/21/2020 5:00:08   9/21/2020 5:51:22   9/21/2020 5:51:36   5777
Routes-Detail.csv   9/21/2020 5:48:37   9/21/2020 5:51:38   9/18/2020 7:28:34   2252
Routes-other.csv    9/18/2020 6:24:52   9/18/2020 7:28:34   9/18/2020 7:28:37   90
Routes.csv  9/21/2020 5:48:36   9/21/2020 5:51:36   9/21/2020 5:51:38   279

As you can see, it failed with a time out on Routes-Detail.

After that, I could no longer get even the simple code in test to run through.

The only difference between Routes-Detail and the other csv's is that there is another page that uses query('Routes-Detail'!$A$3:$Z,"SELECT") and vlookups to format it out.

Any notion why these are timing out? If it is the other sheet recalculating - is there a way to disconnect those queries during the update?

(note - uploadID is a const declared up above with the id of the folder Google Backup & Sync backs up from my work computer, getSheetName() simply removes the .csv from the file name, I use a preformatted master sheet because the default color scheme kills my eyes)

(also, how do I format the data from the spreadsheet better?)

Thanks for any insight.

EDIT - This is definitely something in updateSheets() that's causing ongoing problems for a time after. The last time I ran it, it paused for 5 minutes on Routes-other before finishing (just under the 360 second timeout).

The .csv's that are being imported come from a legacy (AS400) system from a sql query running on a scheduled (or triggered by an email, depending on the query) powershell script.

None of them are overly large.

Is there a better way to automate the import? I've added the code to only update if the file is new (I intend to put this script on a time trigger).