A paragraph break as in Contemporary English Version would be helpful at this point.

Likewise also the king, after convening a great banquet to celebrate these events may be rendered “Philopator also held a big feast to celebrate what had happened.” This verse speaks of a separate celebration that the king arranged.

Gave thanks to heaven unceasingly and lavishly: Heaven, of course, refers to God. So we may translate this whole phrase as “could not stop giving thanks to God repeatedly [or, over and over]” or “kept on giving thanks to God again and again.”

For the unexpected rescue which he had experienced may be rendered “for not putting him to death as he would have expected.” There is a serious textual problem here. A few manuscripts have “they” instead of he. Both Hanhart and Rahlfs have the pronoun “he” in their Greek text, which Anderson and Hadas follow. Emmet accepts the reading with the pronoun “they,” and so does Contemporary English Version. We prefer the pronoun he. More manuscripts have it, and it is the more difficult reading of the two, which often indicates that it is the original. According to this reading, Philopator realized that not only were the Jews rescued, but he himself was, since the God who protected his people from harm allowed the king who intended to kill them to remain alive. Whatever reading is accepted in the text, a footnote should be added for the alternative.

Here are possible models for this verse:

• Meanwhile the king also held a big feast to celebrate what had happened. God had not put him to death, as he might been expected,* and so he could not stop giving thanks to God, over and over.
* God had not put him to death, as he might have expected; other manuscripts could be translated God had rescued the Jews.

• Meanwhile the king also held a big feast to celebrate what had happened. He could not stop thanking God again and again, because God had not put him to death as he might have expected.*
* God had not put him to death as he might have expected; other manuscripts could be translated God had rescued the Jews.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 3-4 Maccabees. (UBS Helps for Translators). Miami: UBS, 2018. For this and other handbooks for translators see here.