I had this issue as well. Support told me that they thought in my case it was Carbonite that might be causing the issue if it created a backup of some of Malwarebytes’ files. I’ll post the part of their email with their instructions for me which solved my problem in case you want try it and see if it helps you:
Step 1 - Safe ModeI have provided the instructions for booting into Safe Mode with networking.
Restart your PC. When you get to the sign-in screen, hold the Shift key down while you select Power > Restart.
After your PC restarts to the Choose an option screen, select Troubleshoot > Advanced options > Startup Settings > Restart.
After your PC restarts, you'll see a list of options. Select 5 or F5 for Safe Modewith Networking.
Step 2 - Clean installLet's perform a clean reinstallation of the latest Malwarebytes for Windows version using our Malwarebytes Support Tool. This is designed to automate the clean uninstallation of our products, along with installation and activation of Malwarebytes for Windows Premium (if applicable). Malwarebytes Support Tool (MBST) Clean Reinstall
If necessary, please redownload MBST using the link below:
Once the file is downloaded, open your Download folder or the location of the downloaded file.
Double-click mb-support-#.#.#.###.exe to run the program.
Click the Advanced menu on the left. Please do not click Start Repair.
Click the Clean button followed by Yes to proceed.
Upon completion, reboot your computer. After the reboot, please wait for the program to reopen.
You will be presented with the option to install Malwarebytes for Windows. Click Yes.
Upon completion, Malwarebytes for Windows will automatically open.