This package update to 1.1.38, in combination with php72 (or perhaps solely due to the php update), results in some graphs "disappearing". The fault is discussed here: https://github.com/Cacti/cacti/issues/1634
It appears there is a data-typing issue involved, and the default poller (cmd.php) raises asserts in places it should not, resulting in the poller "spike killing" the data retrieved. Thus, the blank graphs and "NaN" returns.
The commentary in that issue thread says it is fixed (and if you look at https://github.com/Cacti/cacti/issues/1663, commenting out the offending assert actions, the problem disappears), but apparently the actual fix was not pulled forward into the port/package on FreeBSD.
Please take a look into this; I've commented out the offending "spike kills" locally, but obviously that's a band-aid.
This should hopefully be fixed by the update to 1.2.0 that was just released.
Please re-open this issue if the symptoms are still reproducible after the 1.2.0 update