S7-1500 driver issue

I’m using Ignition version 8.1.13 on a S7-1500 PLC. One of the PLC’s datablocks have up to 1200 variables, first half DINT, second half REAL. In the REAL part of the datablock I’m experiencing the following issue: suppose you have var1 at address offset 460 and var2 at address offset 464. From time to time var2 freezes and get no more updates, while TIA Portal (Siemens PLC software) shows var2 updates correctly. When that happens, in order to get var2 updates I have to issue the restart command on the variable. No errors are shown in Ignition logs, nor in the variable diagnostic.
I tried a workaround, creating a separte S7-1500 device, just to read that only variable, but with no sucess.

Any suggestion?

Tanks in advance, regards

Since VAR2 is the pressure in mbar, whereas VAR1 is the same pressure in Pascal, we decided to change VAR2 to an expression tag, i.e. VAR1/100. The same behaviour is affecting VAR2 too, even if it is an expression tag now. VAR1 is something like 1.23E-4 and VAR2 should be something like 1.23E-6. Question: has Ignition any known issues in handling so small float values?