Common reasons for prism layers missing are twofold: it is either related to the "Minimum Thickness...
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Common reasons for prism layers missing are twofold: it is either related to the "Minimum Thickness Percentage" (MTP), or to the usage of the embedded thin mesher.
The "Minimum Thickness Percentage" (MTP) is a property of the Prism Layer Mesher either in the Mesh Continuum or in the Automated Mesh Operation (AMO),
The default value is 10% of the globally set "Prism Layer Total Thickness" in the AMO, that is, if this is set to 4 mm, for example the limit for the minimum allowed prism layer height is 0.4 mm in all parts added to this AMO. If you now add a custom control for certain surfaces that defines a prism layer height below this value, for example 0.25 mm, the prism layers will be retracted to zero due to MTP.
This situation can happen in relatively large domains including small parts, like Marine or Ground Transportation.
There are basically two workarounds possible:
Reduce the MTP to smaller values like 1% or less to avoid the retraction of the layers.
Specify the global mesh parameters to fit to the small parts and create custom controls for the large portions of the domain.