After a large amount of testing, I have determined that your mod version Thaumic_Gadgets_1.12.2_0.1.5.1_tb.26 causes mods that convert the minecraft auto-jump into step-up to stop working. This includes the mods StepUp and StepupFixer - there may well be others, but these are all i've tested. Vanilla auto-jump itself is not affected and continues to work if the StepUp mods are not installed and yours is.
After a large amount of testing, I have determined that your mod version Thaumic_Gadgets_1.12.2_0.1.5.1_tb.26 causes mods that convert the minecraft auto-jump into step-up to stop working. This includes the mods StepUp and StepupFixer - there may well be others, but these are all i've tested. Vanilla auto-jump itself is not affected and continues to work if the StepUp mods are not installed and yours is.