Decay Mode and Training Phases

That means your TL (training load) is enough to maintain your TP but you haven’t fully validated your signature values during that time.
See this post for details –
MPA on Endurance Rides - General - Xert Community Forum (xertonline.com)

Reference – Breaking Through the Xert Way! – Xert (baronbiosys.com)
Examples – Let’s See Some Recent BT’s - General - Xert Community Forum (xertonline.com)