Normally, licorice gouramis don’t die by a rising pH but by illness. But the rising pH can lead to illness. Not because of the pH but because of a grossly rising amount of germs.
Therefore it is necessary to identify the cause of the rising pH; Deepin’Peat gives some possible explanations. But I like to add that the most frequent cause of dying licorice gouramies is Oodinium that is much suppressed by a low germ concentration in a pH below 7 and much developed by a quickly rising concentration in a pH above 7.
And one should further know that a presence of these noxious little beings is hardly or not at all to be seen during the first one or two weeks. We see them on the fish’s skin only later (if we look at them very closely), but when we see them it’s mostly too late. This is a common experience of the most experienced breeders.
Therefore: Do every thing to prevent a pH rising above 7.0, better above 6.0. The most important reason to take care for a low pH in the tanks of our fish is that they are evolutionarily accustomed to such an often very low pH for just this avoidance of germs that cannot live in this milieu.