Thanks for your posting and considering Aspose.Cells.
We are afraid, we could not replicate this issue with simple excel file in multiple threads. So please provide us your source excel file which is causing this exception.
We need your source excel file that threw this exception because it seems, this is not a thread related issue and your thread was blocked because something went wrong in Aspose.Cells API because of your excel file. This issue may also be replicable in console application.
at java.text.DecimalFormat.format(DecimalFormat.java:596)
- waiting to lock <0x000000050f56c488> (a java.text.DigitList)
at java.text.DecimalFormat.format(DecimalFormat.java:525)
at java.text.NumberFormat.format(NumberFormat.java:286)
at com.aspose.cells.a.c.zp.a(Unknown Source)
at com.aspose.cells.a.c.zp.a(Unknown Source)
at com.aspose.cells.a.d.zfi.a(Unknown Source)
at com.aspose.cells.a.d.zfi.a(Unknown Source)
at com.aspose.cells.a.d.zet.b(Unknown Source)
at com.aspose.cells.a.d.zet.a(Unknown Source)
at com.aspose.cells.a.d.zer.a(Unknown Source)
at com.aspose.cells.a.d.zew.a(Unknown Source)
at com.aspose.cells.a.d.zu.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zq.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zp.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zb.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zb.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zb.a(Unknown Source)
at com.aspose.cells.a.d.zd.a(Unknown Source)
at com.aspose.cells.a.d.zo.a(Unknown Source)
at com.aspose.cells.zap.a(Unknown Source)
at com.aspose.cells.a.d.zew.a(Unknown Source)
at com.aspose.cells.zbwl.a(Unknown Source)
at com.aspose.cells.zbwl.a(Unknown Source)
at com.aspose.cells.zbwl.a(Unknown Source)
at com.aspose.cells.Workbook.a(Unknown Source)
at com.aspose.cells.Workbook.save(Unknown Source)
at com.aspose.cells.Workbook.save(Unknown Source)