Phone line goes red with a line through it for a second or two

Phone line goes red with a line through it for a second or two intermittently, then appears to be fine. It’s the only Grandstream 2170; the rest of the phones are Polycom IP550’s and do not exhibit the same behavior. What can I do in FreePBX and/or Asterisk to determine the cause?

What do you mean goes red with a line through for a second? On the screen of the phone, if yes then it is a hardware issue, you should contact Grandstream.

Yes, on the phone screen itself…like it does normally when the system is rebooted and is not connected yet or when it’s not registered correctly.

Can you post a photo with the screen showing the problem?

That may be difficult since it only happens intermittently and for a few seconds before going green again. The client has gone home for the day, but I will contact her tomorrow morning (Thursday) and ask her to try to get a picture of it. As previously stated, the BLF of the client’s own line on the screen (Grandstream GXP2170) goes red. I’ve seen this happen when setting up phones when the server is rebooting, or when I’ve accidentally put the incorrect port number in the phone settings when registering it.
Thanks for your attention and efforts to help thus far.