The fact that you asked for feedback is a great achievement. Congratulations!
Now, you need to act on it. Since you cannot understand what is wrong, you need help (as you already understand).
The simplified approach is like this:
Accept the feedback. If they see you in some way, that is how they see you - even if you do not like it.
Ask them if they agree to help you improve. I assume that they will agree to some extent.
Ask them to tell you the "worst" things, that you need to concentrate first on improving. Ask them to tell you:
a) what you do bad;
b) what they expect (better).
Now you can more easily see the difference.
Modify your behavior in the direction expected by them - which is also suitable for you.
Repeat from 3.
Note: As a "favor" from them to you, ask them to provide feedback at the moment when you do something wrong (or as soon as possible), so you can understand yourself better. This is especially useful if the negative feedback is about your visible behavior. It might be less helpful if it is about the results of your work - but it still applies there also.
In a comment you said:
I'm already a very hard-working person.
Being hard-working is good, but being good-quality-working is better - and often it can even be done without working so hard. You know the saying, about doing more with less...
I'm beginning to wonder why I should go above and beyond if this is the kind of feedback I receive.
Whose "above and beyond"? What is good for you, might not be good for someone else. You need to satisfy your "customers" (manger, Scrum master, colleagues...)
I found the feedback to be vague and not very relevant to my situation. Even though my Scrum Master has noticed some changes
That is good news - you are doing some changes and people notice the result! You now go on and continue - and apply what I wrote above. Things will only get better. No need for depression.
NOTE (personal experience)
I had a problem (among others) with the tone of my voice. It occasionally sounded aggressive. While many (?) people were bothered, only one person actually told me what was the problem. And I did just as I wrote above: I asked the person to tell me that my voice sound angry at the moment when I talked, not after 30 min or 2 days later. It took quite a long time until I succeeded to hear my voice "from the outside". And did it sound aggressive! And that happened when I answered "3 o'clock" when my manager (imagine!) asked what is the time. Ever since, I am very careful with my voice - and even if I occasionally fail to control it, at least it happens less often, and I can hear myself, and I have a chance to apologize for sounding aggressive.