Unfortunately, since the migration from play-services-ads-lite to play-services-ads-api that happened in v24, this field is no longer accessible.
The funny thing is that it is actually creating, but not referenced. See the decompiled code of AdSize class in play-services-ads-api:24.3.0
static {
new AdSize(-3, 0, "search_v2");
}
while on play-services-ads-lite:23.6.0 it was correctly referenced:
@NonNull
public static final AdSize SEARCH = new AdSize(-3, 0, "search_v2");
This might be related to Proguard/R8 optimization if this field is not actually referenced in your codebase, and no other rule explicitly keep it.
Please take a look and provide a fix.