Hello and welcome to Apple Support Communities, mikaelcedergren.
It looks like your Magic Trackpad is randomly becoming unresponsive, especially when dragging files or using Adobe Photoshop. I rely on my Magic Trackpad every single day so I can certainly understand why you would reach out for help when yours isn't working as expected.
You mentioned that you are running El Capitan on your Mac, which is awesome to hear. The first thing I recommend doing is making sure that you're completely up to date with El Capitan. The most up-to-date version is 10.11.5. If you aren't already familiar with how to update, you can view the steps in the following support article:
Update the software on your Mac
Once you have updated, test out your trackpad. If you're still experience the same issues, we have some additional troubleshooting steps you can try which are specific to what's happening with your Magic Trackpad. Take a look at those steps using the support article listed below:
If your Apple wireless mouse, keyboard, or trackpad aren't working as expected
Since there is a good chance that the issue you're experiencing is software related, the next steps we would recommend are to help narrow things down a bit. Follow these steps, testing your Magic Trackpad after each one:
1. Test in a new user account:
Create a test user account
- From the Apple menu, choose System Preferences.
- Click the Users & Groups icon in the System Preferences window.
- Click the lock icon, then enter an administrator name and password.
- Click the Add button (+) below the list of users.
- Choose a type of user from the New Account pop-up menu.
- Give the user a full name, account name, and password.
- Click OK.
- Close the System Preferences window.
If there are documents from your original user account that you want to test with, place a copy of these items in the Shared folder in the Users folder. Press the Option key while dragging a file to this folder to create a copy.
Log in to the test user account
Log out of your current user account by choosing Log Out from the Apple menu, then log in to the new account you created. If you're prompted to sign in with your iCloud account or Apple ID when you log in, skip this step.
How to test an issue in another user account on your Mac
2. Test in safe mode:
Starting up in safe mode may help you diagnose problems you’re having with your Mac.
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Choose Apple menu > Shut Down.
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After your Mac shuts down, wait 10 seconds, then press the power button.
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Immediately after you hear the startup tone, hold down the Shift key.
You should press the Shift key as soon as possible after you hear the startup tone, but not before.
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Release the Shift key when you see the gray Apple logo and progress indicator.
OS X El Capitan: Start up in safe mode
3. Restart your Mac again but don't hold down any keys during startup. Test out your Magic Trackpad again once it's restarted.
If your Magic Trackpad is still becoming unresponsive after following all of the steps above and you need further assistance, reply back letting us know if you experienced the same issues while booted in the new user account and while booted in safe mode.
Thanks for using Apple Support Communities.
Take care!