How to set up Warmup followed by ReduceLRonPlateau?

I want to linearly increase my learning rate using LinearLR followed by using ReduceLROnPlateau.
I assumed we could use SequentialLR to achieve the same as below

            warmup_scheduler = torch.optim.lr_scheduler.LinearLR(
                self.model_optim, start_factor=0.05, end_factor=1, total_iters=3
            reduce_lrop_scheduler = torch.optim.lr_scheduler.ReduceLROnPlateau(
            lr_scheduler = torch.optim.lr_scheduler.SequentialLR(
                schedulers=[warmup_scheduler, reduce_lrop_scheduler],

As expected, the LR goes up from almost 0 and reaches a constant value, but then when I hit the first milestone, I get an error saying ReduceLROnPlateau doesn’t have an attribute called get_last_lr.
Full error below:

  File "/home/<user>/miniconda3/envs/pyt/lib/python3.9/site-packages/pytorch_lightning/core/", line 1560, in lr_scheduler_step
  File "/home/<user>/miniconda3/envs/pyt/lib/python3.9/site-packages/torch/optim/", line 647, in step
    self._last_lr = self._schedulers[idx].get_last_lr()
AttributeError: 'ReduceLROnPlateau' object has no attribute 'get_last_lr'

I’m using PyTorch lightning to handle the optimisation but I assume the problem lies in incompatibility of ReduceLROnPlateau with SequentialLR. I looked around in different forums but couldn’t find a satisfactory answer.
Side note: I’d like the final learning rate to be 3e-5 after the warmup so I set the initial LR as 3e-5 and end_factor as 1 with initial factor being 0.05. This results in the final lr after warm up to be 1.5e-6 which is off by a factor of 20. I don’t quite understand why this happens, help on that would also be appreciated.

I’m on torch version 1.11.0+cu113, and pytorch-lightning version 1.6.4