Could be a few reasons:

Clear the cookies/cache, they cause these issues

Are you using the qb app?  It is not great.

Try a private window in the browser, that will let you know if it is a cookie issue

Resolution for 'cookie issue issue: 'Can you explain why since the Dec 2016 update, the screen keeps turning grey and becoming unresponsive, forcing me to shut down the program and then log back in?' available: Yes.

The cookie issue issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the cookie issue issue yourself by looking for a resolution described in the article. If it is a complex cookie issue issue or you are unable to solve the issue, you may contact us by clicking here or by using other cookie issue support options.

For more information about resolving issues related to cookie issue in Quickbooks/QBO or to get support for the issue 'Can you explain why since the Dec 2016 update, the screen keeps turning grey and becoming unresponsive, forcing me to shut down the program and then log back in?', click the link below: