Let's perform some troubleshooting solutions to get this sorted out, Himanshu Goya.

There are times when a browser's cache data becomes full of frequent access to web pages or damaged. This causes odd behavior switching accounts in QuickBooks Online (QBO). To better isolate this issue, let's try signing in to your account using a private or incognito window. This mode doesn't use the existing cache data and helps us confirm browser-related issues. Here's how:

• For Google Chrome browser: Ctrl + Shift + N
• For Mozilla Firefox browser: Ctrl + Shift + P
• For Safari browser: Command + Option + P

Then, try switching between developer accounts and existing companies again. If it works, go back to your regular browser and clear the cache to delete those temporarily stored files and browsing history. The overtime collection of data can create corruption, however, removing this should fix the issue. You can also use supported, up-to-date browsers to roll out the possibility of a browser-related issue. 

Feel free to visit our Account Management page for insights about managing your Intuit accounts. 

I'd like to know how you get on after trying the steps as I want to ensure this is resolved for you. Just reply to this post and I'll get back to you. Take care always.