Calc takes 5min opening this one 500KB ODS file?

Hi, first time here, but been using LibreOffice for 2 years now.

Today I woke up to a very annoying problem: One of my spreadsheet files (.ods) that I use everyday is taking forever to load or save. When I open it, LibreOffice Calc lunches and start loading this file, going unresponsive for 5~10min, then the file is finally loaded. Same happens when I save it.

Here are some points I managed to work:

  1. Opening LibreOffice Calc itself is normal, as well as making new files.
  2. All my other spreadsheet files work fine as usual, all .ODS.
  3. Yesterday this file was normal (as I said, I use it everyday).
  4. Getting my months old backup behaved the same.
  5. Even the file on my laptop behaves the same.
  6. Changing the file location and name had no effect.
  7. Was using version 5.1.3, updated to, problem persists.
  8. Tried clearing 4/user and 4/cache folders, no difference.
  9. Converting the file to .XLSX and then saving again as .ODS seems to solve the problem.

Unfortunately I am loosing a lot of formatting this way. Will take me a couple hours going through the file and fixing everything (as well as it does not solve the problem itself, it is just a work around).

Any ideas of what might be happening? Anyone ever had a similar issue? What bugs me the most is that even my backup files behave the same, even in a different computer! Both Windows 7 64 Bits and Windows 8 64 Bits (2nd computer).

Thank you.