The doubling has landed on the wrong side of the stress
stress-doubleA doubled consonant marks a short stressed vowel in English. Reticulate has one of those, but the word never took the doubling.
heard asretticulate
spelledreticulate
saidri-TIK-yuu-lut
One t. reticulate.
English doubles the consonant that comes after a short stressed vowel, not the one before it. Here the stressed vowel is the i, and the consonant after it is the c. Doubling the t marks the unstressed re- instead, which is the quietest part of the word.
The rest of the net
ruticulate retikulate reticculate reticulete raticulate reticulute
The complete set is one click away. All 11 spellings of reticulate.