It happened twice, both in a spreadsheet (personal finance) created 1 year ago ("file1") and in a spreadsheet created using release 184.108.40.206 ("file2).
In the case of file1, all cell references to cells in the previous sheet have been dropped but the values have (temporarily?) remained unchanged (e.g. on the sheet "December", cell reference "=November.H32" has changed to "=H32), the value however has remained unchanged. Fearing losing all file info, I re-referenced other sheet cells 2 days ago without any further drop of spreadsheet indication.
In the case of file2, spreadsheet indication vanished but the values changed to the values of the referenced cells on the same sheet.
Since I am extremely busy, I downloaded and installed release 220.127.116.11 which I used without problems before updating to 18.104.22.168
Dear friends, thank you very much for your attention. I hope that this info will be helpful.
Hardware: HP ProBook 4530s, 8 GB RAM
Operating System: Windows 7 Home Premium 64-bit SP1
Probably duplicate of bug 79441. See also bug 87010, bug 86916, bug 86125.
Please try https://bugs.freedesktop.org/show_bug.cgi?id=87010#c2 (or 4.3.5 rc)
Feel free to reopen if it does not solve the problem for you.
*** This bug has been marked as a duplicate of bug 79441 ***