The spanner in a frozen product is in its freezing😑.....the type of freezing machinery - whether plate or blast freezer or IQF and many other such considerations....
For each type of freezing apparatus the procedure will vary.....if u give some information regarding this then perhaps better suggestions can be offered .
The above will determine the shelflife , not microbial but textural shelf life , and I suspect this is where the problem is - texture / breakage problem while toasting.
Apart from above , the freeze thaw stability of the product should be impeccable ....the entire formulation has to be rendered freeze thaw stable by employing suitable hydrocolloids .