Hello there, @Anonymous.

Due to variations in printers, the design of invoices, checks, or reports may be altered when printed. Additionally, there may be instances where printing becomes problematic. However, there's no need to worry, as we have customized solutions to address specific printing issues.

That being said, allow me to assist you in preventing your checks from being double-sided so you can successfully print them. Please follow these steps I've narrowed down for your convenience:

1. Open any Report. 
2. Hit on the print icon on the report to open the Print Settings.
3. Choose Presets then select either Last Used Setting or Default Setting, whichever one wasn't selected before. If you don't see Presets, select Show Details.
4. When done, close the report and print the check again.

I'll be adding this article for a detailed step-by-step process and to know how to fix other print issues: Troubleshoot printing in QuickBooks Desktop for Mac.

If the problem continues, it's possible that there's an issue with the data in your company file, which is causing the reconciled transactions to disappear. I suggest using the Verify and Rebuild utility. This tool scans for data issues in the company file and automatically fixes them.

Beforehand, make sure your QuickBooks Desktop is up-to-date. This way, you always have its latest features and fixes.

Follow the steps below on how to verify data:

1. On the top menu, click File.
2. Choose Utilities.
3. Select Verify Data.
4. Click OK when QuickBooks doesn't detect any problem with your data.
5. If Verify finds an issue with your data, you'll be prompted to Rebuild Now or View Errors.
6. Click Close or View Errors and take note of the specific error message.

Next, here's how to rebuild data:

1. On the top menu, click File.
2. Choose Utilities.
3. Select Rebuild Data then click OK to close all windows.
4. QuickBooks will prompt you to create a backup before rebuilding your company file. Choose OK to proceed with the backup, or select Cancel to skip the backup and continue rebuilding.
5. Run Rebuild Data again to make sure there's no error.
   - If you haven't set up any backup preferences in QuickBooks, you will be prompted to update them. Simply select Backup Preference, make any necessary edits, and then choose OK.
   - Once the backup process is complete, you can either select Show in Finder to find the backup file or choose OK if you're finished.
6. Once the rebuild's finished, select OK.

Additionally, I've included an article that'll help you learn how to add an electronic signature for checks and paychecks: Create and use electronic signature for checks and paychecks in QuickBooks Desktop for Mac.

Please don't hesitate to post your concerns here in the Community or leave a reply below if you need further assistance printing your checks in QuickBooks Desktop for Mac. It would be my pleasure to ensure a smooth process for you. Take care.