You need to realize that essentially bond pricing reflects the present value of all cash flows you expect from the bond. For long term bonds especially, this makes it a particularly risky book, because you are very sensitive to interest rate changes.
If the interest rate goes up while you are holding your low interest bonds, that means that your future cash flow from the bond (the repayment) is literally worth less than what it was. Your bond payments have a lower real value due to the higher interest rate of the surrounding environment and the increasing price levels, despite being the same nominal amount. That's why the bond's price plummets in the market, which is why this is a solvency crisis: because the assets really are not good for the liabilities at present value, which is the only kind of valuation that makes sense here.
If the interest rate goes up while you are holding your low interest bonds, that means that your future cash flow from the bond (the repayment) is literally worth less than what it was. Your bond payments have a lower real value due to the higher interest rate of the surrounding environment and the increasing price levels, despite being the same nominal amount. That's why the bond's price plummets in the market, which is why this is a solvency crisis: because the assets really are not good for the liabilities at present value, which is the only kind of valuation that makes sense here.