Oscillation of Episode Q0 during DDPG training

How do I interpret this kind of Episode Q0 oscillation?

The oscillation shows a pattern like up and down and the range also increases quite regularly.

According to other docs, they're saying the Q0 is supposed to approach actual discounted future reward as long as the critic network is designed properly.

Is this kind of Q0 oscillation just evidence that my critic network is not well-designed?

Is there any solution to work it out?

I'm not sure this question is acceptable to this community because I think it's more or less a theoretical issue.

[Heesu Kim]

As a side note, I'm using DDPG + LSTM model that RL toolbox provides