Lost IRS in-flight / GPS ONLY

[tvrrr]

Hello,

Sometimes during cruise (usually not on the first but on subsequent legs) I will lose all navigational capability including heading. Looking at the IRS status, all is blank (see attached screenshot). 

This has happened at least three times now, so I've paid extra attention to the steps taken during turnaround. I've consistently reset the FMC by cycling databases, and then entering the GNSS1 position in the POS INIT page. Shutting down all power to the aircraft and starting cold & dark also did not prevent this from happening.

I am aware of the Realignment IRUs Immediately option but of course I would like to avoid this from happening in the first place. I'm sure I'm doing something wrong, but I cannot figure it out... Any help from someone more experienced would be greatly appreciated!

[Pils]

Please provide your Log.txt from an occurrence, thanks.

P.S.

3 hours ago, tvrrr said:

entering the GNSS1 position in the POS INIT page

This isn’t necessary. The IRUs will aligned based on GPS position, if available,  automatically.