I remembered there is an article on this website, so this is the link for this:
https://www.mympnteam.com/resources/pain-and-mp...

I found a clear and simple explanation of why we experience bone pain in MPNs:
"In normal people bone marrow is confined to the central skeleton (cranium, ribs, sternum, vertebrae, and pelvis). The long bones contain mostly fat. In MPN, the bone marrow expands outward to the long bones and can be seen even out in the fingers and toes when bone marrow scanning is done.
The proliferation within the bone marrow cavity may cause pressure inside the bone that, in turn, causes inflammation of the covering of the bone (periostium).
The resulting periostitis may be painful. In some patients with bone and joint pain treatment with myelosuppressive therapy has decreased or eliminated these symptoms by reducing the amount of bone marrow in the cavity and reducing the pressure that it causes."
https://www.pvreporter.com/bone-joint-pain-mpn-...

And there are studies on abdominal and bone pain as symptoms present in MPNs:
"Chronic pain (abdominal, bone) is a prevalent and undermanaged feature of MPN disorders. Chronic non-MPN pain is further complicated by the development of the disorder. Many MPN patients lack understanding on its prevalence and furthermore feel ill-equipped to manage it. Patients have, however, found symptomatic benefit from various pharmacological and non-pharmacological treatment modalities that require further exploration. Results from this study suggest MPN patients should be assessed regularly for pain and offered early referral to specialized services for evaluation, source identification and treatment."
https://www.sciencedirect.com/science/article/p...

I hope this helps understanding this issue more.

Pain and MPNs: Causes and Management | myMPNteam

https://www.mympnteam.com/resources/pain-and-mpns-causes-and-management

Bone & Joint Pain In MPN Patients Explained | Proliferative | PV Reporter

https://www.pvreporter.com/bone-joint-pain-mpn-explained/

just experienced this while on a business trip. Wondering if it from stress. Because of our blood issue I am always worried a heart attack though.