Inventory Quantity Adjustment. Only 300 lines. How can I see more lines?

I can provide some steps so you'll be able to see more lines in the inventory quantity adjustment page, @user210.

In QuickBooks Online you can add more than 300 lines on the inventory quantity adjustment page. Since this isn't your case, I recommend accessing your account on a private window and process it from there. This can help us identify if the issue has something to do with the browser that you're using.

Doing this prevents the browser from collecting cache files (cookies), and also disables any features or benefits gained from already-collected files. Since these files can often become outdated or corrupted, using a Private Window allows you to access QuickBooks with a fresh slate to see if it resolves the issue.

You should be able to add more than 300 lines as you can see in the sample snip attached: 

It it works fine, I suggest clearing your regular browser's cache. The next time you log in to QuickBooks Online, your browser will download fresh copies of your data. Any cache-related issues will be fixed.

On the other hand, please know that QuickBooks' performance decreases as the size of the company file increases. A large number of data may hinder you from adding some more items. You might lessen the inventory quantity adjustment and create a new one.

Let me know how this work for you. I'll be right here to lend a helping hand if you need anything else. Have a lovely day!