I recommend that you clear your browser cookies and cache. Then after you are done, clearing your browser cookies and cache, reinstall the Gmail add-on. I have provided step-by-step instructions below:
1) Clear your browser cookies and cache:
On your computer, open Chrome.
At the top right, click More (Button with Three Dots).
ClickMore tools Clear browsing data.
At the top, choose a time range. To delete everything, selectAll time.
Next to "Cookies and other site data" and "Cached images and files," check the boxes.
Open the new Microsoft Edge and then selectSettings and more >Settings >Privacy and services.
UnderClear browsing data, selectChoose what to clear.
UnderTime range, choose a time range.
SelectCookies and other site data, and then selectClear now.
Click the menu button and selectPreferences.
Select thePrivacy & Securitypanel and go to theCookies and Site Datasection.
Click theClear Data…button. The Clear Data dialog will appear.
Cookies and Site Data (to remove login status and site preferences) and Cached Web Content (to remove stored images, scripts, and other cached content) should both be check marked.
2) Re-install Gmail Add-on
From your Gmail account, click thewhite plus sign (+) iconon the righthand sidebar. When you hover over the plus sign, you’ll see “Get Add-ons.”
Search forDropbox for Gmail. Select it.
Follow the prompts. You may need to log in to your Dropbox account if you aren’t already logged in.
The Add-on will appear in your Gmail account on the righthand sidebar, above the white plus sign (+) icon when you open an email with attachments or with Dropbox or Google Drive links.
I hope this helps!
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