I came up with this minimal example - it is a bit different but the behavior is also not as expected I think:

import numpy as np
import plotly.express as px
from clearml import Task

task = Task.init(project_name='MyProject', task_name='task1', 
                 task_type=Task.TaskTypes.training)
logger = task.get_logger()
y_pred = np.random.rand(100)
y_test = np.random.rand(100)
fig = px.line({'y_pred': y_pred, 'y_test': y_test})
logger.report_plotly(title=f'Forecast', series=f'Forecast', iteration=0, figure=fig)

I executed this code twice with just changing the task_name to 'task2'.
Server version is WebApp: 3.17.1-1039